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  • richardmitnick 9:02 am on March 15, 2019 Permalink | Reply
    Tags: "Can entangled qubits be used to probe black holes?", JQI at UMD, , Quantum entanglement, ,   

    From UC Berkeley: “Can entangled qubits be used to probe black holes?” 

    From UC Berkeley

    March 6, 2019
    Robert Sanders
    rlsanders@berkeley.edu

    1
    Someday, entangled quantum bits, or qubits, may allow us to explore the mysterious interior of a black hole, as represented in this artistic rendering. (Graphic by E. Edwards/Joint Quantum Institute)

    Physicists have used a seven-qubit quantum computer to simulate the scrambling of information inside a black hole, heralding a future in which entangled quantum bits might be used to probe the mysterious interiors of these bizarre objects.

    Scrambling is what happens when matter disappears inside a black hole. The information attached to that matter — the identities of all its constituents, down to the energy and momentum of its most elementary particles — is chaotically mixed with all the other matter and information inside, seemingly making it impossible to retrieve.

    This leads to a so-called “black hole information paradox,” since quantum mechanics says that information is never lost, even when that information disappears inside a black hole.

    So, while some physicists claim that information falling through the event horizon of a black hole is lost forever, others argue that this information can be reconstructed, but only after waiting an inordinate amount of time — until the black hole has shrunk to nearly half its original size. Black holes shrink because they emit Hawking radiation, which is caused by quantum mechanical fluctuations at the very edge of the black hole and is named after the late physicist Stephen Hawking.

    Unfortunately, a black hole the mass of our sun would take about 10^67 years to evaporate — far, far longer than the age of the universe.

    2
    Can you extract information from a black hole? As part of a thought experiment, Alice, a physicist, drops a qubit into a black hole and asks whether Bob can reconstruct the qubit using only the outgoing Hawking radiation. (Graphic by Emily Elisa Edwards, University of Maryland)

    However, there is a loophole — or rather, a wormhole — out of this black hole. It may be possible to retrieve this infalling information significantly faster by measuring subtle entanglements between the black hole and the Hawking radiation it emits.

    Two bits of information — like the quantum bits, or qubits, in a quantum computer — are entangled when they are so closely linked that the quantum state of one automatically determines the state of the other, no matter how far apart they are. Physicists sometimes refer to this as “spooky action at a distance,” and measurements of entangled qubits can lead to the “teleportation” of quantum information from one qubit to another.

    “One can recover the information dropped into the black hole by doing a massive quantum calculation on these outgoing Hawking photons,” said Norman Yao, a UC Berkeley assistant professor of physics and a faculty scientist at Lawrence Berkeley National Laboratory. “This is expected to be really, really hard, but if quantum mechanics is to be believed, it should, in principle, be possible. That’s exactly what we are doing here, but for a tiny three-qubit `black hole’ inside a seven-qubit quantum computer.”

    By dropping an entangled qubit into a black hole and querying the emerging Hawking radiation, you could theoretically determine the state of a qubit inside the black hole, providing a window into the abyss.

    Yao, who is a member of Berkeley Lab’s Quantum Algorithms Team, and his colleagues at the University of Maryland and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, will report their results in a paper appearing in the March 7 issue of the journal Nature.

    Teleportation

    Yao, who is interested in understanding the nature of quantum chaos, learned from friend and colleague Beni Yoshida, a theorist at the Perimeter Institute, that recovering quantum information falling into a black hole is possible if the information is scrambled rapidly inside the black hole. The more thoroughly it is mixed throughout the black hole, the more reliably the information can be retrieved via teleportation. Based on this insight, Yoshida and Yao proposed last year an experiment to provably demonstrate scrambling on a quantum computer.

    3
    A seven-qubit quantum computer circuit built by University of Maryland physicists uses quantum teleportation to detect information scrambling. This is analogous to information propagation through a traversable wormhole, which would allow Bob to identify the qubit that Alice threw into the black hole. (Graphic by Emily Elisa Edwards, University of Maryland)

    “With our protocol, if you measure a teleportation fidelity that is high enough, then you can guarantee that scrambling happened within the quantum circuit,” Yao said. “So, then we called up my buddy, Chris Monroe.”

    Monroe, a physicist at the University of Maryland in College Park who heads one of the world’s leading trapped-ion quantum information groups, decided to give it a try. His group implemented the protocol proposed by Yoshida and Yao and effectively measured an out-of-time-ordered correlation function.

    Called OTOCs, these peculiar correlation functions are created by comparing two quantum states that differ in the timing of when certain kicks or perturbations are applied. The key is being able to evolve a quantum state both forward and backward in time to understand the effect of that second kick on the first kick.

    Monroe’s group created a scrambling quantum circuit on three qubits within a seven-qubit trapped-ion quantum computer and characterized the resulting decay of the OTOC. While the decay of the OTOC is typically taken as a strong indication that scrambling has occurred, to prove that they had to show that the OTOC didn’t simply decay because of decoherence — that is, that it wasn’t just poorly shielded from the noise of the outside world, which also causes quantum states to fall apart.

    Yao and Yoshida proved that the greater the accuracy with which they could retrieve the entangled or teleported information, the more stringently they could put a lower limit on the amount of scrambling that had occurred in the OTOC. This is because, if information is successfully teleported from one atom to another, it means that the state of the first atom is spread out across all of the atoms — something that only happens if the information is scrambled. If the information was lost, successful teleportation would not be possible. For an arbitrary process whose scrambling properties might not be known, this method could be used to test whether — or even how much — it scrambles.

    Monroe and his colleagues measured a teleportation fidelity of approximately 80 percent, meaning that perhaps half of the quantum state was scrambled and the other half decayed by decoherence. Nevertheless, this was enough to demonstrate that genuine scrambling had indeed occurred in this three-qubit quantum circuit.

    “One possible application for our protocol is related to the benchmarking of quantum computers, where one might be able to use this technique to diagnose more complicated forms of noise and decoherence in quantum processors,” Yao said. “The ability to diagnose how noise affects quantum simulations is key to building better fault-tolerant algorithms and getting accurate answers from current noisy quantum computers.”

    Yao is also working with a UC Berkeley group led by Irfan Siddiqi to demonstrate scrambling in a different quantum system, superconducting qutrits: quantum bits that have three, rather than two, states. Siddiqi is a UC Berkeley professor of physics and a faculty scientist at Berkeley Lab, where he is leading the effort to build an advanced quantum computing test bed.

    “At its core, this is a qubit or qutrit experiment, but the fact that we can relate it to cosmology is because we believe the dynamics of quantum information is the same,” he said. “The U.S. is launching a billion-dollar quantum initiative, and understanding the dynamics of quantum information connects many areas of research within this initiative: quantum circuits and computing, high energy physics, black hole dynamics, condensed matter physics and atomic, molecular and optical physics. The language of quantum information has become pervasive for our understanding of all these different systems.”

    “Regardless of whether real black holes are very good scramblers, studying quantum scrambling in the lab could provide useful insights for the future development of quantum computing or quantum simulation,” Monroe said.

    Aside from Yao, Yoshida and Monroe, other co-authors are graduate student Tommy Schuster of UC Berkeley and graduate student and first author Kevin Landsman, Caroline Figgatt and Norbert Linke of Maryland’s Joint Quantum Institute. The work was supported by the Department of Energy’s Office of Advanced Scientific Computing Research and Office of High Energy Physics and National Science Foundation.

    RELATED INFORMATION

    Ion experiment aces quantum scrambling test (JQI)
    Verified Quantum Information Scrambling (Nature) [above]
    Disentangling Scrambling and Decoherence via Quantum Teleportation (Physical Review X)
    Norman Yao’s website

    See the full article here .

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  • richardmitnick 4:19 pm on March 6, 2019 Permalink | Reply
    Tags: An atom-defect hybrid quantum system, , , Coherence in quantum behavior, If you can see things on smaller scales with better sensitivity than anybody else you’re going to find new physics, In the experiment we will have an atom on the diamond surface that couples to a shallow subsurface NV center inside the material in a highly controlled cryogenic and ultra-high vacuum environment, Key to this technology is the nitrogen-vacancy (NV) center in diamond an extensively studied point defect in diamond’s carbon atom lattice, , Quantum entanglement, , , The physical and materials knowledge gained by mastering the interface of such a hybrid system would contribute to the development of quantum computing systems, The technique is reminiscent of molecular beam epitaxy (MBE) a method of “growing” a material atom-by-atom on a substrate, This project is a “natural fit” for UC Santa Barbara say the researchers due to the campus’s strengths in both physics and materials sciences, To Hold Without Touching, UCSB- University of California Santa Barbara   

    From UC Santa Barbara: “Sensing Disturbances in the Force” 

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    From UC Santa Barbara

    March 5, 2019
    Sonia Fernandez

    UC Santa Barbara researchers receive U.S. Department of Energy grant to build atom-defect hybrid quantum sensor.

    1

    It will be a feat of engineering and physics at the smallest scales, but it could open the biggest doors — to new science and more advanced technologies. UC Santa Barbara physicists Ania Jayich and David Weld, and materials scientist Kunal Mukherjee, are teaming up to build an atom-defect hybrid quantum system — a sensor technology that would use the power of quantum science to unlock the mysteries of the atomic and subatomic world.

    “We’re at this tipping point where we know there’s a lot of impactful and fundamentally exciting things we can do,” said Jayich, whose research investigates quantum effects at the nanoscale. The $1.5 million grant from the Department of Energy’s Office of Basic Sciences will kickstart the development of a system that will allow researchers an unusually high level of control over atoms while simultaneously leaving their “quantumness” untouched.

    “In this whole field of quantum technology, that has been the big challenge,” Jayich said. In the quirky and highly unintuitive world of quantum mechanics, she explained, objects can exist in a superposition of many places at once, and entangled elements separated by thousands of miles can be inextricably linked — phenomena which, in turn, have opened up new and powerful possibilities for areas such as sensing, computing and the deepest investigations of nature.

    However, the coherence that is the signature of these quantum behaviors — a state of information that is the foundation of quantum technology — is exceedingly fragile and fleeting.

    “Quantum coherence is such a delicate phenomenon,” Jayich said. “Any uncontrolled interaction with the environment will kill it. And that’s the whole challenge behind advancing this field — how do we preserve the very delicate quantumness of an atom or defect, or anything?” To study a quantum element such as an atom, one would have to interrogate it, she explained, but the act of measuring can also destroy its quantum nature.

    To Hold Without Touching

    Fortunately, Jayich and colleagues see a way around this conundrum.

    “It’s a hybrid atomic- and solid-state system,” Jayich said. Key to this technology is the nitrogen-vacancy (NV) center in diamond, an extensively studied point defect in diamond’s carbon atom lattice. The NV center is comprised of a vacancy created by a missing carbon atom next to another vacancy that is substituted with a nitrogen atom. With its several unpaired electrons, it is highly sensitive to and interactive with external perturbations, such as the minute magnetic or electric fields that would occur in the presence of individual atoms of interest.

    “In the proposed experiment, we would have an atom on the diamond surface that couples to a shallow, subsurface NV center inside the material, in a highly controlled, cryogenic and ultra-high vacuum environment,” Jayich explained. The diamond surface provides a natural trapping that allows researchers to more easily hold the atom in place — a challenge for many quantum scientists who want to trap individual atoms. Further, upon reading the state of the defect, one could understand the quantum properties of the atom under interrogation — without touching the atom itself and destroying its coherence.

    Previous methods aimed at interrogating individual adatoms (adsorbed atoms) relied on passing current through the atoms and necessitated metal surfaces, both of which, according to Jayich, reduce quantum coherence times.

    “The past several decades of work in atomic physics have resulted in tools that allow exquisite quantum control of all degrees of freedom of atomic ensembles, but typically only when the atoms are gently held in a vacuum far away from all other matter,” added Weld. “This experiment seeks to extend this level of control into a much messier but also much more technologically relevant regime, by manipulating and sensing individual atoms that are chemically bonded to a solid surface.”

    With the hybrid system, Jayich said, it would be “very easy to talk to the NV center defect with light, and the atoms have the benefit of retaining quantum information for very long periods of time. So we have a system where we leverage the best of both worlds — the best of the atom and the best of the defect — and put them together in a way that’s functional.”

    A Foundation for Future Quantum Tech

    Looking forward, the state-of-the-art spatial resolution and sensitivity of this atom-defect hybrid quantum system could offer researchers the deepest look at the workings of individual atoms, or structures of molecules at nanometer- and Angstrom scales.

    “If you can see things on smaller scales with better sensitivity than anybody else, you’re going to find new physics,” Jayich said. The connections of microscopic structure to macroscopic behavior in materials synthesis could be elucidated. Quantum phenomena in condensed matter systems could be probed. Proteins that have evaded structural determination — such as membrane proteins — could be studied.

    This project is a “natural fit” for UC Santa Barbara, say the researchers, due to the campus’s strengths in both physics and materials sciences. The technique is reminiscent of molecular beam epitaxy (MBE), a method of “growing” a material atom-by-atom on a substrate.

    “There is a strong tradition of materials deposition at UCSB, ranging from metals, semiconductors to novel electronic materials,” Mukherjee said of the campus’s long record of materials growth and world-class MBE facilities. Among the first few atoms they intend to study are rare-earth types such as holmium or dysprosium “as they have unpaired electrons which are protected from environmental interactions by the atomic structure,” noted Mukherjee, adding that he is “particularly excited” about the challenge of removing the atoms from and resetting the diamond surface without breaking vacuum.

    Additionally, the physical and materials knowledge gained by mastering the interface of such a hybrid system would contribute to the development of quantum computing systems. According to Jayich, future practicable quantum computers would likely be a hybrid of several elements, similar to how conventional computers are a mix of magnetic, electronic and solid-state components.

    See the full article here .


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    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

     
  • richardmitnick 11:49 am on March 1, 2019 Permalink | Reply
    Tags: "Yale researchers create a ‘universal entangler’ for new quantum tech", Potential uses in quantum computing and cryptography and quantum communications, Quantum entanglement, , The entangling mechanism is called an exponential-SWAP gate,   

    From Yale University: “Yale researchers create a ‘universal entangler’ for new quantum tech” 

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    From Yale University

    February 27, 2019
    Jim Shelton

    One of the key concepts in quantum physics is entanglement, in which two or more quantum systems become so inextricably linked that their collective state can’t be determined by observing each element individually. Now Yale researchers have developed a “universal entangler” that can link a variety of encoded particles on demand.

    The discovery represents a powerful new mechanism with potential uses in quantum computing, cryptography, and quantum communications. The research is led by the Yale laboratory of Robert Schoelkopf and appears in the journal Nature.

    Quantum calculations are accomplished with delicate bits of data called qubits, which are prone to errors. To implement faithful quantum computation, scientists say, they need “logical” qubits whose errors can be detected and rectified using quantum error correction codes.

    “We’ve shown a new way of creating gates between logically-encoded qubits that can eventually be error-corrected,” said Schoelkopf, the Sterling Professor of Applied Physics and Physics at Yale and director of the Yale Quantum Institute. “It’s a much more sophisticated operation than what has been performed previously.”

    The entangling mechanism is called an exponential-SWAP gate. In the study, researchers demonstrated the new technology by deterministically entangling encoded states in any chosen configurations or codes, each housed in two otherwise isolated, 3D superconducting microwave cavities.

    1
    Yale researchers have created a way to entangle a variety of encoded particles on demand.

    “This universal entangler is critical for robust quantum computation,” said Yvonne Gao, co-first author of the study. “Scientists have invented a wealth of hardware-efficient, quantum error correction codes — each one cleverly designed with unique characteristics that can be exploited for different applications. However, each of them requires wiring up a new set of tailored operations, introducing a significant hardware overhead and reduced versatility.”

    The universal entangler mitigates this limitation by providing a gate between any desired input states. “We can now choose any desired codes or even change them on the fly without having to re-wire the operation,” said co-first author Brian Lester.

    The discovery is just the latest step in Yale’s quantum research work. Yale scientists are at the forefront of efforts to develop the first fully useful quantum computers and have done pioneering work in quantum computing with superconducting circuits.

    Additional authors of the study are Kevin Chou, Luigi Frunzio, Michel Devoret, Liang Jiang, and Steven Girvin. The research was supported by the U.S. Army Research Office.

    See the full article here .

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    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

     
  • richardmitnick 12:24 pm on January 27, 2019 Permalink | Reply
    Tags: Anything that happens to one photon in an entangled pair will be transferred to the other one as well, , , , Fourth Industrial Revolution, Inquire-Quantum Information Research and Engineering instrument, Quantum communication is a secure method of sending and receiving data that's designed to preclude eavesdropping, Quantum entanglement, Quantum Information and Materials Group, , , Ultrasensitive cameras see things at the single photon level   

    From University of Arizona: “Interdisciplinary UA Researchers Get Tangled Up in Quantum Computing” 

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    From University of Arizona

    Jan. 25, 2019
    Emily Dieckman

    UA researchers are building a quantum hub known as Inquire, which will be the world’s first shared research and training instrument to help researchers in diverse fields benefit from quantum resources.

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    Conceptual artwork of a pair of entangled quantum particles interacting. (Photo: Mark Garlick/Science Photo Library)

    Good neighbors often share resources: a cup of sugar, extra lawn chairs, a set of jumper cables. Researchers across campus at the University of Arizona will soon be able to share a less common – and far more valuable – resource to help them further their research: entangled photons, or interlinked pairs of light particles.

    With approximately $1.4 million in funding – $999,999 from the National Science Foundation and about $400,000 from the UA – professor Zheshen Zhang is leading the construction of the Interdisciplinary Quantum Information Research and Engineering instrument, known as Inquire, at the UA. Inquire is the world’s first shared research and training instrument to help researchers in diverse fields – including those with no expertise in quantum information science – benefit from quantum resources.

    Zhang is an assistant professor of materials science and engineering and optical sciences, and the leader of the Quantum Information and Materials Group at the UA. The co-investigators of the Inquire project include Ivan Djordjevic, professor of electrical and computer engineering and optical sciences; Jennifer Barton, director of the BIO5 Institute and professor of biomedical engineering, biosystems engineering, electrical and computer engineering, and optical sciences; Nasser Peyghambarian, professor of optical sciences; and Marek Romanowski, associate professor of biomedical engineering, and materials science and engineering.

    A network of fiber-optic cables will connect an automated quantum information hub in the basement of the Electrical and Computer Engineering building to four other buildings on campus: Biosciences Research Labs, Mines and Metallurgy, Physics and Atmospheric Sciences, and Meinel Optical Sciences.

    “One of the joys of the UA is collaborating with top scholars working in cutting-edge fields,” Barton said. “It seems like science fiction, but Zheshen is building a facility that will create quantum-entangled photons, then deliver them via fiber optics halfway across campus, right into the Translational Bioimaging Resource in the Biosciences Research Labs building.”

    “This is an exciting project that perfectly represents some of the key themes underlying our strategic plan,” said UA President Robert C. Robbins. “To be a leader in the Fourth Industrial Revolution, we must leverage collaboration, stay ahead of the technology curve and provide a high-powered environment where researchers have the tools they need to solve the world’s grand challenges. I look forward to seeing the new opportunities this facility brings once it is completed.”

    Construction on the project already has begun. The expected completion date is September 2021.

    Seeing Individual Photons

    Much like an atom is the smallest unit of matter, a photon is the smallest unit of light. So, while we can see the light of tens of billions of photons in a room lit by a lamp or a courtyard lit by the sun, the human eye – and most microscopes – can’t see individual photons. But sometimes this too-small-to-see information can be important. For example, a biomedical engineering lab might be doing an imaging study on a protein or an organic molecule that’s emitting a signal too weak for traditional cameras to see.

    “You can send your photons to the core facility, which is equipped with an array of ultrasensitive cameras that can see things at the single photon level,” Zhang said.

    Traditionally, researchers used high-powered lasers to illuminate these biological samples, which were sometimes damaged in the process. Using entangled photons as an illumination source provides higher sensitivity, less illuminating power, and the same – or even higher – resolution.

    “Two entangled photons can be worth a million of their classical brethren, potentially allowing us to image deeper without harming tissue,” Barton said.

    High-Precision Probing

    These fiber-optic cables are a two-way street. Researchers can send their photons into the central hub to be imaged by the high-tech microscopes, but the center can also share entangled photons with labs across campus.

    Entangled photons are interlinked pairs. Even when they’re separated by large distances, anything that happens to one photon in an entangled pair will be transferred to the other one as well.

    This relationship has several uses. For example, researchers can use photons as probes to help determine the nature of unidentified materials. The changes a material introduces to a photon, such as a change in color, provide clues to the material’s identity. When one entangled photon in a pair is used as a probe, the material introduces changes to both photons in the entangled pair.

    “Now you can perform a measurement on both photons to learn about the sample being probed,” Zhang said. “You can have twice as much information about the way the material is affecting the photon.”

    Secure Communications

    Entangled photons can also be used in quantum communication, a secure method of sending and receiving data that’s designed to preclude eavesdropping. It works like this: Before Party A shares any sensitive information with Party B, Party A sends a “quantum key,” a series of entangled photons that serves as the code for decrypting future transmissions. Quantum keys are designed so that the very act of decrypting or reading their contents changes their contents.

    If the quantum key arrives with any parts decrypted, the communicating parties know not to use that part of the key to encrypt future transmissions, because it has been “read” by hackers. The communicating parties can simply cut out that part of the key and use a new, shorter quantum key they know is secure.

    Party A and Party B in the above example don’t need to be quantum information scientists. Researchers across all kinds of disciplines can benefit from the unique features of entangled photons, and Inquire’s aim is to allow for just that.

    “This is a key area that the National Science Foundation identifies as one of its 10 Big Ideas and really wants to push forward because it is so interdisciplinary,” Zhang said. “It involves researchers across the boundaries of science, engineering, computer science, physics, chemistry, math, optics – everywhere. The key question is ‘How can everybody speak the same language, and how can they benefit from the progress made in other areas?'”

    See the full article here .


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    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium?

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    An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 1:22 pm on January 21, 2019 Permalink | Reply
    Tags: , , , , Quantum entanglement,   

    From Max Planck Gesellschaft: “Flying optical cats for quantum communication” 

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    From Max Planck Gesellschaft

    January 21, 2019

    An entangled atom-light state realizes a paradoxical thought experiment by Erwin Schrödinger.

    1
    Dead and alive: Schrödinger’s cat is entangled with an atom. If the atom is excited, the cat is alive. If it has decayed, the cat is dead. In the experiment, a light pulse represents the two states (peaks) and may be in a superposition of both, just like the cat. © Christoph Hohmann, Nanosystems Initiative Munich (NIM)

    An old thought experiment now appears in a new light. In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. A group of researchers led by Gerhard Rempe, Director of the Department of Quantum Dynamics at the Max Planck Institute of Quantum Optics, has now realized an optical version of Schrödinger’s thought experiment in the laboratory. In this instance, pulses of laser light play the role of the cat. The insights gained from the project open up new prospects for enhanced control of optical states, that can in the future be used for quantum communications.

    “According to Schrödinger‘s idea, it is possible for a microscopic particle, such as a single atom, to exist in two different states at once. This is called a superposition. Moreover, when such a particle interacts with a macroscopic object, they can become ‘entangled’, and the macroscopic object may end up in superposition state. Schrödinger proposed the example of a cat, which can be both dead and alive, depending on whether or not a radioactive atom has decayed – a notion which is in obvious conflict with our everyday experience,” Professor Rempe explains.

    In order to realize this philosophical gedanken experiment in the laboratory, physicists have turned to various model systems. The one implemented in this instance follows a scheme proposed by the theoreticians Wang and Duan in 2005. Here, the superposition of two states of an optical pulse serves as the cat. The experimental techniques required to implement this proposal – in particular an optical resonator – have been developed in Rempe’s group over the past few years.

    A test for the scope of quantum mechanics

    The researchers involved in the project were initially skeptical as to whether it would be possible to generate and reliably detect such quantum mechanically entangled cat states with the available technology. The major difficulty lay in the need to minimize optical losses in their experiment. Once this was achieved, all measurements were found to confirm Schrödinger’s prediction. The experiment allows the scientists to explore the scope of application of quantum mechanics and to develop new techniques for quantum communication.

    The laboratory at the Max Planck Institute in Garching is equipped with all the tools necessary to perform state-of-the-art experiments in quantum optics. A vacuum chamber and high-precision lasers are used to isolate a single atom and manipulate its state. At the core of the set-up is an optical resonator, consisting of two mirrors separated by a slit only 0.5 mm wide, where an atom can be trapped. A laser pulse is fed into the resonator and reflected, and thereby interacts with the atom. As a result, the reflected light gets entangled with the atom. By performing a suitable measurement on the atom, the optical pulse can be prepared in a superposition state, just like that of Schrödinger’s cat. One special feature of the experiment is that the entangled states can be generated deterministically. In other words, a cat state is produced in every trial.

    “We have succeeded in generating flying optical cat states, and demonstrated that they behave in accordance with the predictions of quantum mechanics. These findings prove that our method for creating cat states works, and allowed us to explore the essential parameters,” says PhD student Stephan Welte.

    A whole zoo of states for future quantum communication

    “In our experimental setup, we have succeeded not only in creating one specific cat state, but arbitrarily many such states with different superposition phases – a whole zoo, so to speak. This capability could in the future be utilized to encode quantum information,” adds Bastian Hacker.

    “Schrödinger‘s cat was originally enclosed in a box to avoid any interaction with the environment. Our optical cat states are not enclosed in a box. They propagate freely in space. Yet they remain isolated from the environment and retain their properties over long distances. In the future we could use this technology to construct quantum networks, in which flying optical cat states transmit information,” says Gerhard Rempe. This underlines the significance of his group’s latest achievement.

    See the full article here .


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    The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

    According to its primary goal, the Max Planck Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014)[2] Max Planck Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

    The Max Planck Institutes focus on excellence in research. The Max Planck Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the Max Planck institutes fifth worldwide in terms of research published in Nature journals (after Harvard, MIT, Stanford and the US NIH). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by the Chinese Academy of Sciences, the Russian Academy of Sciences and Harvard University. The Thomson Reuters-Science Watch website placed the Max Planck Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.

     
  • richardmitnick 4:47 pm on November 6, 2018 Permalink | Reply
    Tags: Physicists Race to Demystify Einstein’s ‘Spooky’ Science, Quantum entanglement,   

    From UC San Diego: “Physicists Race to Demystify Einstein’s ‘Spooky’ Science” 

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    From UC San Diego

    August 20, 2018

    Cynthia Dillon
    858-822-0142
    cdillon@ucsd.edu

    International research team recasts timeline, dating from the Big Bang, of possible quantum theory alternatives.

    When it comes to fundamental physics, things can get spooky. At least that’s what Albert Einstein said when describing the phenomenon of quantum entanglement—the linkage of particles in such a way that measurements performed on one particle seem to affect the other, even when separated by great distances. “Spooky action at a distance” is how Einstein described what he couldn’t explain.

    1
    Schematic of the 2018 “Cosmic Bell” experiment at the Roque de Los Muchachos Observatory in the Canary Islands, where two large telescopes observed the fluctuating color of light from distant quasars (red and blue galaxies). The green beams indicate polarization-entangled photons sent through the open air between stations separated by about one kilometer. Image by Andrew S. Friedman and Dominik Rauch.

    While quantum mechanics includes many mysterious phenomena like entanglement, it remains the best fundamental physical theory describing how matter and light behave at the smallest scales. Quantum theory has survived numerous experimental tests in the past century while enabling many advanced technologies: modern computers, digital cameras and the displays of TVs, laptops and smartphones. Quantum entanglement itself is also the key to several next-generation technologies in computing, encryption and telecommunications. Yet, there is no clear consensus on how to interpret what quantum theory says about the true nature of reality at the subatomic level, or to definitively explain how entanglement actually works.

    2
    Diagram of a run of the Cosmic Bell test. The regions of space and time where an alternative, non-quantum mechanism could still have acted (limited to the red and/or blue regions) corresponds to at least 7.78 billion years ago (blue region). Light from the more distant quasar was emitted 12.21 billion years ago (red region). Compared to the gray region, representing all of space and time prior to the experiment, the alternatives are limited to within four percent of the space-time volume since the Big Bang. Image by Andrew Friedman and David Leon.

    According to Andrew Friedman, a research scientist at the University of California San Diego Center for Astrophysics and Space Sciences (CASS), “the race is on” around the globe to identify and experimentally close potential loopholes that could still allow alternative theories, distinct from quantum theory, to explain perplexing phenomena like quantum entanglement. Such loopholes could potentially allow future quantum encryption schemes to be hacked. So, Friedman and his fellow researchers conducted a “Cosmic Bell” test with polarization-entangled photons designed to further close the “freedom-of-choice” or “free will” loophole in tests of Bell’s inequality, a famous theoretical result derived by physicist John S. Bell in the 1960s. Published in the Aug. 20 issue of Physical Review Letters, their findings are consistent with quantum theory and push back to at least 7.8 billion years ago the most recent time by which any causal influences from alternative, non-quantum mechanisms could have exploited the freedom-of-choice loophole.

    “Our findings imply that any such mechanism is excluded from explaining the results from within a whopping 96% of the space-time volume in the causal past of our experiment, stretching all the way from the Big Bang until today,” said Friedman. “While these alternatives to quantum theory have not been completely ruled out, we are pushing them into a progressively smaller corner of space and time.”

    In their experiment, the researchers outsourced the choice of entangled photon measurements to the universe. They did this by using the color of light that has been traveling to Earth for billions of years from distant galaxies—quasars—as a “cosmic random number generator.”

    “This is a rare experiment that comes along only very seldomly in a scientist’s career: a pioneering experiment that sets the bar so high few, if any, competitors can ever match it,” noted UC San Diego astrophysicist Brian Keating. “I’m so proud that my graduate student David Leon had the chance to make a significant contribution to this fascinating research, co-led by CASS research scientist, Dr. Andrew Friedman.”

    Besides UC San Diego’s Friedman and Leon, the full research team included lead author and Ph.D. student Dominik Rauch, along with Anton Zeilinger and his experimental quantum optics group from the University of Vienna; theoretical physicists David Kaiser and Alan Guth at MIT; Jason Gallicchio and his experimental physics group at Harvey Mudd College, and others. Expanding upon their previous quantum entanglement experiments [Physical Review Letters], Friedman and colleagues went to great effort to choose entangled particle measurements using 3.6 and 4.2 meter telescopes in the Canary Islands, allowing them to collect sufficient light from the much fainter, distant quasars.

    To conduct their test, they shined laser light into a special crystal that generated pairs of entangled photons, which the scientists repeatedly sent through the open air toward both telescopes. From the quasar light collected, the scientists could choose polarization measurement settings while each entangled photon was in mid-flight. The group was allotted three nights and a few hours at the Roque de los Muchachos Observatory in La Palma, amidst operationally challenging conditions including freezing rain, high winds, and uncertainty about whether they would have enough time to complete the experiment. Additionally, Friedman and colleagues had to write software that could choose the best quasars to observe on-the-fly—from a database of more than 1.5 million—and predict the observation time needed to obtain a statistically significant result.

    “We pushed to the limit what could be done within the time constraints,” said Friedman. “The experiment would not have been possible without an amazing international collaboration. It was a roller coaster experience to see it actually work.”

    The research was funded by the Austrian Academy of Sciences; The Austrian Science Fund with SFB F40 (FOQUS) and project COQuS (W1210-N16); the Austrian Federal Ministry of Education, Science and Research; the University of Vienna (via the project QUESS); the National Science Foundation INSPIRE Grant (PHY-1541160); the U.S. Department of Energy (DE-SC0012567); the U.S. Department of Defense, through the National Defense Science & Engineering Graduate Fellowship Program, and UC San Diego’s Ax Center for Experimental Cosmology.

    See the full article here .

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    UC San Diego Campus

    The University of California, San Diego (also referred to as UC San Diego or UCSD), is a public research university located in the La Jolla area of San Diego, California, in the United States.[12] The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha).[13] Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. UC San Diego is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. UC San Diego was ranked 8th among public universities and 37th among all universities in the United States, and rated the 18th Top World University by U.S. News & World Report ‘s 2015 rankings.

     
  • richardmitnick 3:56 pm on November 6, 2018 Permalink | Reply
    Tags: “Cosmic Bell” experiment at the Roque de Los Muchachos Observatory in the Canary Islands, Quantum entanglement,   

    From Symmetry: “The quest to test quantum entanglement” 

    Symmetry Mag
    From Symmetry

    11/06/18
    Laura Dattaro

    Quantum entanglement, doubted by Einstein, has passed increasingly stringent tests.

    Quantum entanglement and spatial distribution Credit Nakagawa et al

    Quantum entanglement By Ishdasrox (Own work) [CC BY-SA 4.0 (via Wikimedia Commons)]

    Over 12 billion years ago, speeding particles of light left an extremely luminous celestial object called a quasar and began a long journey toward a planet that did not yet exist. More than 4 billion years later, more photons left another quasar for a similar trek. As Earth and its solar system formed, life evolved, and humans began to study physics, the particles continued on their way. Ultimately, they landed in the Canary Island of La Palma in a pair of telescopes set up for an experiment testing the very nature of reality.

    1
    Schematic of the 2018 “Cosmic Bell” experiment at the Roque de Los Muchachos Observatory in the Canary Islands, where two large telescopes observed the fluctuating color of light from distant quasars (red and blue galaxies). The green beams indicate polarization-entangled photons sent through the open air between stations separated by about one kilometer. Credit: Andrew S. Friedman and Dominik Rauch

    The experiment was designed to study quantum entanglement, a phenomenon that connects quantum systems in ways that are impossible in our macro-sized, classical world. When two particles, like a pair of electrons, are entangled, it’s impossible to measure one without learning something about the other. Their properties, like momentum and position, are inextricably linked.

    “Quantum entanglement means that you can’t describe your joint quantum system in terms of just local descriptions, one for each system,” says Michael Hall, a theoretical physicist at the Australian National University.

    Entanglement first arose in a thought experiment worked out by none other than Albert Einstein. In a 1935 paper, Einstein and two colleagues showed that if quantum mechanics fully described reality, then conducting a measurement on one part of an entangled system would instantaneously affect our knowledge about future measurements on the other part, seemingly sending information faster than the speed of light, which is impossible according to all known physics. Einstein called this effect “spooky action at a distance,” implying something fundamentally wrong with the budding science of quantum mechanics.

    Decades later, quantum entanglement has been experimentally confirmed time and again. While physicists have learned to control and study quantum entanglement, they’ve yet to find a mechanism to explain it or to reach consensus on what it means about the nature of reality.

    “Entanglement itself has been verified over many, many decades,” says Andrew Friedman, an astrophysicist at University of California, San Diego, who worked on the quasar experiment, also known as a “cosmic Bell test.” “The real challenge is that even though we know it’s an experimental reality, we don’t have a compelling story of how it actually works.”

    Bell’s assumptions

    The world of quantum mechanics—the physics that governs the behavior of the universe at the very smallest scales—is often described as exceedingly weird. According to its laws, nature’s building blocks are simultaneously waves and particles, with no definite location in space. It takes an outside system observing or measuring them to push them to “choose” a definitive state. And entangled particles seem to affect one another’s “choices” instantaneously, no matter how far apart they are.

    Einstein was so dissatisfied with these ideas that he postulated classical “hidden variables,” outside our understanding of quantum mechanics, that, if we understood them, would make entanglement not so spooky. In the 1960s, physicist John Bell devised a test for models with such hidden variables, known as “Bell’s inequality.”

    Bell outlined three assumptions about the world, each with a corresponding mathematical statement: realism, which says objects have properties they maintain whether they are being observed or not; locality, which says nothing can influence something far enough away that a signal between them would need to travel faster than light; and freedom of choice, which says physicists can make measurements freely and without influence from hidden variables. Probing entanglement is the key to testing these assumptions. If experiments show that nature obeys these assumptions, then we live in a world we can understand classically, and hidden variables are only creating the illusion of quantum entanglement. If experiments show that the world does not follow them, then quantum entanglement is real and the subatomic world is truly as strange as it seems.

    “What Bell showed is that if the world obeys these assumptions, there’s an upper limit to how correlated entangled particle measurements can be,” Friedman says.

    Physicists can measure properties of particles, such as their spin, momentum or polarization. Experiments have shown that when particles are entangled, the outcome of these measurements are more statistically correlated than would be expected in a classical system, violating Bell’s inequalities.

    In one type of Bell test, scientists send two entangled photons to detectors far apart from one another. Whether the photons reach the detectors depends on their polarization; if they are perfectly aligned, they will pass through, but otherwise, there is some probability they will be blocked, depending on the angle of alignment. Scientists look to see whether the entangled particles wind up with the same polarization more often than could be explained by classical statistics. If they do, at least one of Bell’s assumptions can’t be true in nature. If the world does not obey realism, then properties of particles aren’t well defined before measurements. If the particles could influence one another instantaneously, then they would somehow be communicating to one another faster than the speed of light, violating locality and Einstein’s theory of special relativity.

    Scientists have long speculated that previous experimental results can be explained best if the world does not obey one or both of the first two of Bell’s assumptions—realism and locality. But recent work has shown that the culprit could be his third assumption—the freedom of choice. Perhaps the scientists’ decision about the angle at which to let the photons in is not as free and random as they thought.

    The quasar experiment was the latest to test the freedom of choice assumption. The scientists determined the angle at which they would allow photons into their detectors based on the wavelength of the light they detected from the two distant quasars, something determined 7.8 and 12.2 billion years ago, respectively. The long-traveling photons took the place of physicists or conventional random number generators in the decision, eliminating earthbound influences on the experiment, human or otherwise.

    At the end of the test, the team found far higher correlations among the entangled photons than Bell’s theorem would predict if the world were classical.

    That means that, if some hidden classical variable were actually determining the outcomes of the experiment, in the most extreme scenario, the choice of measurement would have to have been laid out long before human existence—implying that quantum “weirdness” is really the result of a universe where everything is predetermined.

    “That’s unsatisfactory to a lot of people,” Hall says. “They’re really saying, if it was set up that long ago, you would have to try and explain quantum correlations with predetermined choices. Life would lose all meaning, and we’d stop doing physics.”

    Of course, physics marches on, and entanglement retains many mysteries to be probed. In addition to lacking a causal explanation for entanglement, physicists don’t understand how measuring an entangled system suddenly reverts it to a classical, unentangled state, or whether entangled particles are actually communicating in some way, mysteries that they continue to explore with new experiments.

    “No information can go from here to there instantaneously, but different interpretations of quantum mechanics will agree or disagree that there’s some hidden influence,” says Gabriela Barreto Lemos, a postdoctoral researcher at the International Institute of Physics in Brazil. “But something we all agree upon is this definition in terms of correlation and statistics.”

    Looking for something strange

    Developing a deeper understanding of entanglement can help solve problems both practical and fundamental. Quantum computers rely on entanglement. Quantum encryption, a theoretical security measure that is predicted to be impossible to break, also requires a full understanding of quantum entanglement. If hidden variables are valid, quantum encryption might actually be hackable.

    And entanglement may hold the key to some of the most fundamental questions in physics. Some researchers have been studying materials with large numbers of particles entangled, rather than simply pairs. When this many-body entanglement happens, physicists observe new states of matter beyond the familiar solid, liquid and gas, as well as new patterns of entanglement not seen anywhere else.

    “One thing it tells you is that the universe is richer than you previously suspected,” says Brian Swingle, a University of Maryland physicist researching such materials. “Just because you have a collection of electrons does not mean that the resulting state of matter has to be electron-like.”

    Such interesting properties are emerging from these materials that physicists are starting to realize that entanglement may actually stitch together space-time itself—a somewhat ironic twist, as Einstein, who first connected space and time in his relativity theory, disliked quantum mechanics so much. But if the theory proves correct, entanglement could help physicists finally reach one of their ultimate goals: achieving a theory of quantum gravity that unites Einstein’s relativistic world with the enigmatic and seemingly contradictory quantum world.

    “It’s important to do these experiments even if we don’t believe we’re going to find anything strange,” Lemos says. “In physics, the revolution comes when we think we’re not going to find something strange, and then we do. So you have to do it.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:47 pm on November 5, 2018 Permalink | Reply
    Tags: , Griffith precision measurement takes it to the limit, , Heisenberg limit, , Quantum computing algorithms, Quantum entanglement,   

    From Griffith University via phys.org: “Griffith precision measurement takes it to the limit” 

    Griffith U bloc

    From Griffith University

    via

    phys.org

    November 5, 2018

    1
    Griffith University researchers have demonstrated a procedure for making precise measurements of speed, acceleration, material properties and even gravity waves possible, approaching the ultimate sensitivity allowed by laws of quantum physics. Credit: Griffith University

    Published in Nature Communications, the work saw the Griffith team, led by Professor Geoff Pryde, working with photons (single particles of light) and using them to measure the extra distance travelled by the light beam, compared to its partner reference beam, as it went through the sample being measured—a thin crystal.

    The researchers combined three techniques—entanglement (a kind of quantum connection that can exist between the photons), passing the beams back and forth along the measurement path, and a specially-designed detection technique.

    “Every time a photon passes through the sample, it makes a kind of mini-measurement. The total measurement is the combination of all of these mini-measurements,” said Griffith’s Dr. Sergei Slussarenko, who oversaw the experiment. “The more times the photons pass through, the more precise the measurement becomes.

    “Our scheme will serve as a blueprint for tools that can measure physical parameters with precision that is literally impossible to achieve with the common measurement devices.

    Lead author of the paper Dr. Shakib Daryanoosh said this method can be used to investigate and measure other quantum systems.

    “These can be very fragile, and every probe photon we send it would disturb it. In this case, using few photons but in the most efficient way possible is critical and our scheme shows how do exactly that,” he said.

    While one strategy is to just use as many photons as possible, that’s not enough to reach the ultimate performance. For that, it is necessary to also extract the maximum amount of measurement information per photon pass, and that is what the Griffith experiment has achieved, coming far closer?to the so-called Heisenberg limit of precision than any comparable experiment.

    The remaining error is due experimental imperfection, as the scheme designed by Dr. Daryanoosh and Professor Howard Wiseman, is capable of achieving the exact Heisenberg limit, in theory.

    “The really nice thing about this technique is that it works even when you don’t have a good starting guess for the measurement,” Prof. Wiseman said. “Previous work has mostly focused a lot on the case where it’s possible to make a very good starting approximation, but that’s not always possible.”

    A few extra steps are required before this proof-of-principle demonstration can be harnessed outside the lab.

    Producing entangled photons is not simple with current technology, and this means it is still much easier to use many photons inefficiently, rather than each set of entangled photons in the best way possible.

    However, according to the team, the ideas behind this approach can find immediate applications in quantum computing algorithms and research in fundamental science.

    The scheme can ultimately be extended to a larger number of entangled photons, where the difference of the Heisenberg limit over the usually achievable limit is more significant.

    See the full article here .

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    Griffith U Campus

    In 1971, Griffith was created to be a new kind of university—one that offered new degrees in progressive fields such as Asian studies and environmental science. At the time, these study areas were revolutionary—today, they’re more important than ever.

    Since then, we’ve grown into a comprehensive, research-intensive university, ranking in the top 5% of universities worldwide. Our teaching and research spans five campuses in South East Queensland and all disciplines, while our network of more than 120,000 graduates extends around the world.

    Griffith continues the progressive traditions of its namesake, Sir Samuel Walker Griffith, who was twice the Premier of Queensland, the first Chief Justice of the High Court of Australia, and the principal author of the Australian Constitution.

     
  • richardmitnick 11:27 am on September 27, 2018 Permalink | Reply
    Tags: , Atom-based quantum computer, , , , Quantum entanglement, , Rubidium atoms, Rydberg state,   

    From Science Magazine: “Arrays of atoms emerge as dark horse candidate to power quantum computers” 

    AAAS
    From Science Magazine

    Sep. 26, 2018
    Sophia Chen

    1
    Lasers are used to trap arrays of atoms within glass chambers made by ColdQuanta, a neutral atom quantum computing startup.
    COLDQUANTA INC.

    In a small basement laboratory, Harry Levine, a Harvard University graduate student in physics, can assemble a rudimentary computer in a fraction of a second. There isn’t a processor chip in sight; his computer is powered by 51 rubidium atoms that reside in a glass cell the size of a matchbox. To create his computer, he lines up the atoms in single file, using a laser split into 51 beams. More lasers—six beams per atom—slow the atoms until they are nearly motionless. Then, with yet another set of lasers, he coaxes the atoms to interact with each other, and, in principle, perform calculations.

    It’s a quantum computer, which manipulates “qubits” that can encode zeroes and ones simultaneously in what’s called a superposition state. If scaled up, it might vastly outperform conventional computers at certain tasks. But in the world of quantum computing, Levine’s device is somewhat unusual. In the race to build a practical quantum device, investment has largely gone to qubits that can be built on silicon, such as tiny circuits of superconducting wire and small semiconductors structures known as quantum dots. Now, two recent studies have demonstrated the promise of the qubits Levine works with: neutral atoms. In one study, a group including Levine showed a quantum logic gate made of two neutral atoms could work with far fewer errors than ever before. And in another, researchers built 3D structures of carefully arranged atoms, showing that more qubits can be packed into a small space by taking advantage of the third dimension.

    The advances, along with the arrival of venture capital funding, suggest neutral atoms could be on the upswing, says Dana Anderson, CEO of ColdQuanta, a Boulder, Colorado–based company that is developing an atom-based quantum computer. “We’ve done our homework,” Anderson says. “This is really in the engineering arena now.”

    Because neutral atoms lack electric charge and interact reluctantly with other atoms, they would seem to make poor qubits. But by using specifically timed laser pulses, physicists can excite an atom’s outermost electron and move it away from the nucleus, inflating the atom to billions of times its usual size. Once in this so-called Rydberg state, the atom behaves more like an ion, interacting electromagnetically with neighboring atoms and preventing them from becoming Rydberg atoms themselves.

    Physicists can exploit that behavior to create entanglement—the quantum state of interdependence needed to perform a computation. If two adjacent atoms are excited into superposition, where both are partially in a Rydberg state and partially in their ground state, a measurement will collapse the atoms to one or the other state. But because only one of the atoms can be in its Rydberg state, the atoms are entangled, with the state of one depending on the state of the other.

    Once entangled, neutral atoms offer some inherent advantages. Atoms need no quality control: They are by definition identical. They’re much smaller than silicon-based qubits, which means, in theory, more qubits can be packed into a small space. The systems operate at room temperature, whereas superconducting qubits need to be placed inside a bulky freezer. And because neutral atoms don’t interact easily, they are more immune to outside noise and can hold onto quantum information for a relatively long time. “Neutral atoms have great potential,” says Mark Saffman, a physicist at the University of Wisconsin in Madison. “From a physics perspective, [they could offer] easier scalability and ultimately better performance.”

    Entangled atoms

    The two new studies bolster these claims. By engineering better quality lasers, Levine and his colleagues, led by physicist Mikhail Lukin at Harvard, were able to accurately program a two-rubidium atom logic gate 97% of the time, they report in a paper published on 20 September in Physical Review Letters. That puts the method closer to the performance of superconducting qubits, which already achieve fidelity rates above 99%. In a second study, published in Nature on 5 September, Antoine Browaeys of the Charles Fabry Laboratory near Paris and his colleagues demonstrated an unprecedented level of control over a 3D array of 72 atoms. To show off their control, they even arranged the atoms into the shape of the Eiffel Tower. Another popular qubit type, ions, are comparably small. But they can’t be stacked this densely because they repel each other, acknowledges Crystal Senko, a physicist at the University of Waterloo in Canada who works on ion quantum computers.

    Not everyone is convinced. Compared with other qubits, neutral atoms tend not to stay put, says Varun Vaidya, a physicist at Xanadu, a quantum computing company in Toronto, Canada, that builds quantum devices with photon qubits. “The biggest issue is just holding onto the atoms,” he says. If an atom falls out of place, Lukin’s automated laser system can reassemble the atoms in less than a second, but Vaidya says this may still prohibit the devices from performing longer tasks. “Right now, nobody knows what’s going to be the best qubit,” Senko says. “The bottom line is, they all have their problems.”

    Still, ColdQuanta has recently received $6.75 million in venture funding. Another startup, Atom Computing, based in Berkeley, California, has raised $5 million. CEO Ben Bloom says the company will pursue qubits made of atoms with two valence electrons instead of rubidium’s one, such as calcium and strontium. Bloom believes these atoms will allow for longer-lived qubits. Lukin says he’s also interested in commercializing his group’s technology.

    The startups, as well as Saffman’s group, are aiming to build fully programmable quantum computers. For now, Lukin wants his group to focus on building quantum simulators, a more limited kind of computer that specializes in solving specific optimization problems by preparing the qubits a certain way and letting them evolve naturally. Levine says his group’s device could, for example, help telecommunications engineers figure out where to put radio towers to minimize cost and maximize coverage. “We’re going to try to do something useful with these devices,” Levine says. “People still don’t know yet what quantum systems can do.”

    In the next year or two, he and his colleagues think neutral atom devices could deliver an answer.

    See the full article here .


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  • richardmitnick 7:35 am on September 7, 2018 Permalink | Reply
    Tags: , Fish-eye lens may entangle pairs of atoms, , , , Quantum entanglement,   

    From MIT News: “Fish-eye lens may entangle pairs of atoms” 

    MIT News
    MIT Widget

    From MIT News

    September 5, 2018
    Jennifer Chu

    1
    James Maxwell was the first to realize that light is able to travel in perfect circles within the fish-eye lens because the density of the lens changes, with material being thickest at the middle and gradually thinning out toward the edges. No image credit.

    Scientists find a theoretical optical device may have uses in quantum computing.

    Nearly 150 years ago, the physicist James Maxwell proposed that a circular lens that is thickest at its center, and that gradually thins out at its edges, should exhibit some fascinating optical behavior. Namely, when light is shone through such a lens, it should travel around in perfect circles, creating highly unusual, curved paths of light.

    He also noted that such a lens, at least broadly speaking, resembles the eye of a fish. The lens configuration he devised has since been known in physics as Maxwell’s fish-eye lens — a theoretical construct that is only slightly similar to commercially available fish-eye lenses for cameras and telescopes.

    Now scientists at MIT and Harvard University have for the first time studied this unique, theoretical lens from a quantum mechanical perspective, to see how individual atoms and photons may behave within the lens. In a study published Wednesday in Physical Review A, they report that the unique configuration of the fish-eye lens enables it to guide single photons through the lens, in such a way as to entangle pairs of atoms, even over relatively long distances.

    Entanglement is a quantum phenomenon in which the properties of one particle are linked, or correlated, with those of another particle, even over vast distances. The team’s findings suggest that fish-eye lenses may be a promising vehicle for entangling atoms and other quantum bits, which are the necessary building blocks for designing quantum computers.

    “We found that the fish-eye lens has something that no other two-dimensional device has, which is maintaining this entangling ability over large distances, not just for two atoms, but for multiple pairs of distant atoms,” says first author Janos Perczel, a graduate student in MIT’s Department of Physics. “Entanglement and connecting these various quantum bits can be really the name of the game in making a push forward and trying to find applications of quantum mechanics.”

    The team also found that the fish-eye lens, contrary to recent claims, does not produce a perfect image. Scientists have thought that Maxwell’s fish-eye may be a candidate for a “perfect lens” — a lens that can go beyond the diffraction limit, meaning that it can focus light to a point that is smaller than the light’s own wavelength. This perfect imaging, scientist predict, should produce an image with essentially unlimited resolution and extreme clarity.

    However, by modeling the behavior of photons through a simulated fish-eye lens, at the quantum level, Perczel and his colleagues concluded that it cannot produce a perfect image, as originally predicted.

    “This tells you that there are these limits in physics that are really difficult to break,” Perczel says. “Even in this system, which seemed to be a perfect candidate, this limit seems to be obeyed. Perhaps perfect imaging may still be possible with the fish eye in some other, more complicated way, but not as originally proposed.”

    Perczel’s co-authors on the paper are Peter Komar and Mikhail Lukin from Harvard University.

    A circular path

    Maxwell was the first to realize that light is able to travel in perfect circles within the fish-eye lens because the density of the lens changes, with material being thickest at the middle and gradually thinning out toward the edges. The denser a material, the slower light moves through it. This explains the optical effect when a straw is placed in a glass half full of water. Because the water is so much denser than the air above it, light suddenly moves more slowly, bending as it travels through water and creating an image that looks as if the straw is disjointed.

    In the theoretical fish-eye lens, the differences in density are much more gradual and are distributed in a circular pattern, in such a way that it curves rather bends light, guiding light in perfect circles within the lens.

    In 2009, Ulf Leonhardt, a physicist at the Weizmann Institute of Science in Israel was studying the optical properties of Maxwell’s fish-eye lens and observed that, when photons are released through the lens from a single point source, the light travels in perfect circles through the lens and collects at a single point at the opposite end, with very little loss of light.

    “None of the light rays wander off in unwanted directions,” Perczel says. “Everything follows a perfect trajectory, and all the light will meet at the same time at the same spot.”

    Leonhardt, in reporting his results, made a brief mention as to whether the fish-eye lens’ single-point focus might be useful in precisely entangling pairs of atoms at opposite ends of the lens.

    “Mikhail [Lukin] asked him whether he had worked out the answer, and he said he hadn’t,” Perczel says. “That’s how we started this project and started digging deeper into how well this entangling operation works within the fish-eye lens.”

    Playing photon ping-pong

    To investigate the quantum potential of the fish-eye lens, the researchers modeled the lens as the simplest possible system, consisting of two atoms, one at either end of a two-dimensional fish-eye lens, and a single photon, aimed at the first atom. Using established equations of quantum mechanics, the team tracked the photon at any given point in time as it traveled through the lens, and calculated the state of both atoms and their energy levels through time.

    They found that when a single photon is shone through the lens, it is temporarily absorbed by an atom at one end of the lens. It then circles through the lens, to the second atom at the precise opposite end of the lens. This second atom momentarily absorbs the photon before sending it back through the lens, where the light collects precisely back on the first atom.

    “The photon is bounced back and forth, and the atoms are basically playing ping pong,” Perczel says. “Initially only one of the atoms has the photon, and then the other one. But between these two extremes, there’s a point where both of them kind of have it. It’s this mind-blowing quantum mechanics idea of entanglement, where the photon is completely shared equally between the two atoms.”

    Perczel says that the photon is able to entangle the atoms because of the unique geometry of the fish-eye lens. The lens’ density is distributed in such a way that it guides light in a perfectly circular pattern and can cause even a single photon to bounce back and forth between two precise points along a circular path.

    “If the photon just flew away in all directions, there wouldn’t be any entanglement,” Perczel says. “But the fish-eye gives this total control over the light rays, so you have an entangled system over long distances, which is a precious quantum system that you can use.”

    As they increased the size of the fish-eye lens in their model, the atoms remained entangled, even over relatively large distances of tens of microns. They also observed that, even if some light escaped the lens, the atoms were able to share enough of a photon’s energy to remain entangled. Finally, as they placed more pairs of atoms in the lens, opposite to one another, along with corresponding photons, these atoms also became simultaneously entangled.

    “You can use the fish eye to entangle multiple pairs of atoms at a time, which is what makes it useful and promising,” Perczel says.

    Fishy secrets

    In modeling the behavior of photons and atoms in the fish-eye lens, the researchers also found that, as light collected on the opposite end of the lens, it did so within an area that was larger than the wavelength of the photon’s light, meaning that the lens likely cannot produce a perfect image.

    “We can precisely ask the question during this photon exchange, what’s the size of the spot to which the photon gets recollected? And we found that it’s comparable to the wavelength of the photon, and not smaller,” Perczel says. “Perfect imaging would imply it would focus on an infinitely sharp spot. However, that is not what our quantum mechanical calculations showed us.”

    Going forward, the team hopes to work with experimentalists to test the quantum behaviors they observed in their modeling. In fact, in their paper, the team also briefly proposes a way to design a fish-eye lens for quantum entanglement experiments.

    “The fish-eye lens still has its secrets, and remarkable physics buried in it,” Perczel says. “But now it’s making an appearance in quantum technologies where it turns out this lens could be really useful for entangling distant quantum bits, which is the basic building block for building any useful quantum computer or quantum information processing device.”

    See the full article here .


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