From Sandia Lab: “Quantum computing steps further ahead with new projects at Sandia”

From Sandia Lab

January 7, 2019

Neal Singer
nsinger@sandia.gov
505-845-7078

Quantum computing is a term that periodically flashes across the media sky like heat lightning in the desert: brilliant, attention-getting and then vanishing from the public’s mind with no apparent aftereffects.

Yet a multimillion dollar international effort to build quantum computers is hardly going away.

Sandia National Laboratories researchers are looking to shape the future of computing through a series of quantum information science projects. As part of the work, they will collaborate to design and develop a new quantum computer that will use trapped atomic ion technology. (Photo by Randy Montoya)

And now, four new projects led by Sandia National Laboratories aim to bring the wiggly subject into steady illumination by creating:

A quantum computing “testbed” with accessible components on which industrial, academic and government researchers can run their own algorithms.
A suite of test programs to measure the performance of quantum hardware.
Classical software to ensure reliable operation of quantum computing testbeds and coax the most utility from them.
High-level quantum algorithms that explore connections with theoretical physics, classical optimization and machine learning.

These three- to five-year projects are funded at $42 million by the Department of Energy’s Office of Science’s Advanced Scientific Computing Research program, part of Sandia’s Advanced Science and Technology portfolio.

Quantum information science “represents the next frontier in the information age,” said U.S. Secretary of Energy Rick Perry this fall when he announced $218 million in DOE funding for the research. “At a time of fierce international competition, these investments will ensure sustained American leadership in a field likely to shape the long-term future of information processing and yield multiple new technologies that benefit our economy and society.”

Partners on three of the four Sandia-led projects include the California Institute of Technology, Los Alamos National Laboratory, Dartmouth College, Duke University, the University of Maryland and Tufts University.

Birth of a generally available quantum computer

Sandia National Laboratories researcher Mohan Sarovar is developing software for quantum testbeds. Sandia’s quantum computer will play a role analogous to those of graphics processing units in today’s high-performance computers. (Photo by Randy Wong)

Design and construction of the quantum computer itself — formally known as the Quantum Scientific Computing Open User Testbed — under the direction of Sandia researcher Peter Maunz, is a $25.1 million, five-year project that will use trapped atomic ion technology.

Trapped ions are uniquely suited to realize a quantum computer because quantum bits (qubits) — the quantum generalization of classical bits — are encoded in the electronic states of individual trapped atomic ions, said Maunz.

“Because trapped ions are identical and suspended by electric fields in a vacuum, they feature identical, nearly perfect qubits that are well isolated from the noise of the environment and therefore can store and process information faithfully,” he said. “While current small-scale quantum computers without quantum error correction are still noisy devices, quantum gates with the lowest noise have been realized with trapped-ion technology.”

A quantum gate is a fundamental building block of a quantum circuit operating on a small number of qubits.

Furthermore, in trapped-ion systems, Maunz said, “It is possible to realize quantum gates between all pairs of ions in the same trap, a feature which can crucially reduce the number of gates needed to realize a quantum computation.”

QSCOUT is intended to make a trapped-ion quantum computer accessible to the DOE scientific community. As an open platform, Maunz said, it will not only provide full information about all its quantum and classical processes, it will also enable researchers to investigate, alter and optimize the internals of the testbed, or even to propose more advanced implementations of the quantum operations.

Because today’s quantum computers only have access to a limited number of qubits and their operation is still subject to errors, these devices cannot yet solve scientific problems beyond the reach of classical computers. Nevertheless, access to prototype quantum processors like QSCOUT should allow researchers to optimize existing quantum algorithms, invent new ones and assess the power of quantum computing to solve complex scientific problems, Maunz said.

Proof of the pudding

Sandia National Laboratories researcher Robin Blume-Kohout is leading a team that will develop a variety of methods to ensure the performance of quantum computers in real-world situations. (Photo by Kevin Young)

But how do scientists ensure that the technical components of a quantum testbed are performing as expected?

A Sandia team led by quantum researcher Robin Blume-Kohout is developing a toolbox of methods to measure the performance of quantum computers in real-world situations.

“Our goal is to devise methods and software that assess the accuracy of quantum computers,” said Blume-Kohout.

The $3.7 million, five-year Quantum Performance Assessment project plans to develop a broad array of tiny quantum software programs. These range from simple routines like “flip this qubit and then stop,” to testbed-sized instances of real quantum algorithms for chemistry or machine learning that can be run on almost any quantum processor.

These programs aren’t written in a high-level computer language, but instead are sequences of elementary instructions intended to run directly on the qubits and produce a known result.

However, Blume-Kohout says, “because we recognize that quantum mechanics is also intrinsically somewhat random, some of these test programs are intended to produce 50/50 random results. That means we need to run test programs thousands of times to confirm that the result really is 50/50 rather than, say, 70/30, to check a quantum computer’s math.”

The team’s goal is to use testbed results to debug processors like QSCOUT by finding problems so engineers can fix them. This demands considerable expertise in both physics and statistics, but Blume-Kohout is optimistic.

“This project builds on what Sandia has been doing for five years,” he said. “We’ve tackled similar problems in other situations for the U.S. government.”

For example, he said, the Intelligence Advanced Research Projects Activity reached out to Sandia to evaluate the results of the performers on its LogiQ program, which aims to improve the fidelity of quantum computing. “We expect be able to say with a certain measure of reliability, ‘Here are the building blocks you need to achieve a goal,’” Blume-Kohout said.

Quantum and classical computing meet up

Once the computer is built by Maunz’s group and its reliability ascertained by Blume-Kohout’s team, how will it be used for computational tasks?

The Sandia-led, $7.8 million, four-year Optimization, Verification and Engineered Reliability of Quantum Computers project aims to answer this question. LANL and Dartmouth College are partners.

Project lead and physicist Mohan Sarovar expects that the first quantum computer developed at Sandia will be a very specialized processor, playing a role analogous to that played by graphics processing units in high-performance computing.

“Similarly, the quantum testbed will be good at doing some specialized things. It’ll also be ‘noisy.’ It won’t be perfect,” Sarovar said. “My project will ask: What can you use such specialized units for? What concrete tasks can they perform, and how can we use them jointly with specialized algorithms connecting classical and quantum computers?”

The team intends to develop classical “middleware” aimed at making computational use of the QSCOUT testbed and similar near-term quantum computers.

“While we have excellent ideas for how to use fully developed, fault-tolerant quantum computers, we’re not really sure what computational use the limited devices we expect to see created in the near future will be,” Sarovar said. “We think they will play the role of a very specialized co-processor within a larger, classical computational framework.” The project aims to develop tools, heuristics and software to extract reliable, useful answers from these near-term quantum co-processors.

At the peak

At the most theoretical level, the year-old, Sandia-led Quantum Optimization and Learning and Simulation (QOALAS) project’s team of theoretical physicists and computer scientists, headed by researcher Ojas Parekh, have produced a new quantum algorithm for solving linear systems of equations — one of the most fundamental and ubiquitous challenges facing science and engineering.

The three-year, $4.5 million project, in addition to Sandia, includes LANL, the University of Maryland and Caltech.

“Our quantum linear systems algorithm, created at LANL, has the potential to provide an exponential speedup over classical algorithms in certain settings,” said Parekh. “Although similar quantum algorithms were already known for solving linear systems, ours is much simpler.

“For many problems in quantum physics we want to know what is the lowest energy state? Understanding such states can, for example, help us better understand how materials work. Classical discrete optimization techniques developed over the last 40 years can be used to approximate such states. We believe quantum physics will help us obtain better or faster approximations.”

The team is working on other quantum algorithms that may offer an exponential speedup over the best-known classical algorithms. For example, said Parekh, “If a classical algorithm required 2100 steps — two times itself one hundred times, or 1,267,650,600,228,229,401,496,703,205,376 steps — to solve a problem, which is a number believed to be larger than all the particles in the universe, then the quantum algorithm providing an exponential speed-up would only take 100 steps. An exponential speedup is so massive that it might dwarf such practical hang-ups as, say, excessive noise.

“Sooner or later, quantum will be faster,” he said.

See the full article here .

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Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

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From MIT News: “Physicists record ‘lifetime’ of graphene qubits”

From MIT News

December 31, 2018
Rob Matheson

Researchers from MIT and elsewhere have recorded the “temporal coherence” of a graphene qubit — how long it maintains a special state that lets it represent two logical states simultaneously — marking a critical step forward for practical quantum computing. Stock image

First measurement of its kind could provide stepping stone to practical quantum computing.

Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit — meaning how long it can maintain a special state that allows it to represent two logical states simultaneously. The demonstration, which used a new kind of graphene-based qubit, represents a critical step forward for practical quantum computing, the researchers say.

Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1. But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks. Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing.

In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials. These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

“Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT. “In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

A pristine graphene sandwich

Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum). In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage. These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches. The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene. The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

How voltage helps

The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip. “Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

See the full article here .

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From RIKEN: “Hybrid qubits solve key hurdle to quantum computing”

From RIKEN

December 28, 2018

Spin-based quantum computers have the potential to tackle difficult mathematical problems that cannot be solved using ordinary computers, but many problems remain in making these machines scalable. Now, an international group of researchers led by the RIKEN Center for Emergent Matter Science have crafted a new architecture for quantum computing. By constructing a hybrid device made from two different types of qubit—the fundamental computing element of quantum computers—they have created a device that can be quickly initialized and read out, and that simultaneously maintains high control fidelity.

Quantum computing – IBM – the current state

In an era where conventional computers appear to be reaching a limit, quantum computers—which do calculations using quantum phenomena—have been touted as potential replacements, and they can tackle problems in a very different and potentially much more rapid way. However, it has proven difficult to scale them up to the size required for performing real-world calculations.

In 1998, Daniel Loss, one of the authors of the current study, came up with a proposal, along with David DiVincenzo of IBM, to build a quantum computer by using the spins of electrons embedded in a quantum dot—a small particle that behaves like an atom, but that can be manipulated, so that they are sometimes called “artificial atoms.” In the time since then, Loss and his team have endeavored to build practical devices.

There are a number of barriers to developing practical devices in terms of speed. First, the device must be able to be initialized quickly. Initialization is the process of putting a qubit into a certain state, and if that cannot be done rapidly it slows down the device. Second, it must maintain coherence for a time long enough to make a measurement. Coherence refers to the entanglement between two quantum states, and ultimately this is used to make the measurement, so if qubits become decoherent due to environmental noise, for example, the device becomes worthless. And finally, the ultimate state of the qubit must be able to be quickly read out.

While a number of methods have been proposed for building a quantum computer, the one proposed by Loss and DiVincenzo remains one of the most practically feasible, as it is based on semiconductors, for which a large industry already exists.

For the current study, published in Nature Communications, the team combined two types of quits on a single device. The first, a type of single-spin qubit called a Loss-DiVincenzo qubit, has very high control fidelity—meaning that it is in a clear state, making it ideal for calculations, and has a long decoherence time, so that it will stay in a given state for a relatively long time before losing its signal to the environment.

Unfortunately, the downside to these qubits is that they cannot be quickly initialized into a state or read out. The second type, called a singlet-triplet qubit, is quickly initialized and read out, but it quickly becomes decoherent. For the study, the scientists combined the two types with a type of quantum gate known as a controlled phase gate, which allowed spin states to be entangled between the qubits in a time fast enough to maintain the coherence, allowing the state of the single-spin qubit to be read out by the fast singlet-triplet qubit measurement.

According to Akito Noiri of CEMS, the lead author of the study, “With this study we have demonstrated that different types of quantum dots can be combined on a single device to overcome their respective limitations. This offers important insights that can contribute to the scalability of quantum computers.”

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From University of New South Wales: “Harnessing the power of ‘spin-orbit’ coupling: scaling up spin-based quantum computation”

From University of New South Wales

10 Dec 2018
Karen Viner-Smith

Research teams from UNSW are investigating multiple pathways to scale up atom-based computing architectures using spin-orbit coupling – advancing towards their goal of building a silicon-based quantum computer in Australia.

Artist’s impression of spin-orbit coupling of atom qubits. Illustration: Tony Melov. Credit: CQC2T

Australian scientists have investigated new directions to scale up qubits utilising their spin-orbit coupling, adding a new suite of tools to the armory.

Spin-orbit coupling, the coupling of the qubits’ orbital and spin degree of freedom, allows the manipulation of the qubit via electric, rather than magnetic fields. Using the electric dipole coupling between qubits means they can be placed further apart, thereby providing flexibility in the chip fabrication process.

In one of these approaches, published in Science Advances, a team of scientists led by UNSW Professor Sven Rogge investigated the spin-orbit coupling of a boron atom in silicon.

“Single boron atoms in silicon are a relatively unexplored quantum system, but our research has shown that spin-orbit coupling provides many advantages for scaling up to a large number of qubits in quantum computing,” says Professor Rogge, Program Manager at the Centre for Quantum Computation and Communication Technology (CQC2T).

Following on from earlier results from the UNSW team, published last month in Physical Review X, Rogge’s group has now focused on applying fast read-out of the spin state (1 or 0) of just two boron atoms in an extremely compact circuit all hosted in a commercial transistor.

“Boron atoms in silicon couple efficiently to electric fields, enabling rapid qubit manipulation and qubit coupling over large distances. The electrical interaction also allows coupling to other quantum systems, opening up the prospects of hybrid quantum systems,” says Rogge.

Phosphorus atom qubits

Another piece of recent research by Prof Michelle Simmons’ team at UNSW has also highlighted the role of spin orbit coupling in atom-based qubits in silicon, this time with phosphorus atom qubits. The research was recently published in npj Quantum Information.

The research revealed surprising results. For electrons in silicon — and in particular those bound to phosphorus donor qubits — spin orbit control was commonly regarded as weak, giving rise to seconds long spin lifetimes. However, the latest results revealed a previously unknown coupling of the electron spin to the electric fields typically found in device architectures created by control electrodes.

“By careful alignment of the external magnetic field with the electric fields in an atomically engineered device, we found a means to extend these spin lifetimes to minutes,” says Professor Michelle Simmons, Director, CQC2T.

“Given the long spin coherence times and the technological benefits of silicon, this newly discovered coupling of the donor spin with electric fields provides a pathway for electrically-driven spin resonance techniques, promising high qubit selectivity,” says Simmons.

Both results highlight the benefits of understanding and controlling spin orbit coupling for large-scale quantum computing architectures.

Commercialising silicon quantum computing IP in Australia

Since May 2017, Australia’s first quantum computing company, Silicon Quantum Computing Pty Limited (SQC), has been working to create and commercialise a quantum computer based on a suite of intellectual property developed at the Australian Centre of Excellence for Quantum Computation and Communication Technology (CQC2T). Its goal is to produce a 10-qubit prototype device in silicon by 2022 as the forerunner to a commercial scale silicon-based quantum computer.

As well as developing its own proprietary technology and intellectual property, SQC will continue to work with CQC2T and other participants in the Australian and International Quantum Computing ecosystems, to build and develop a silicon quantum computing industry in Australia and, ultimately, to bring its products and services to global markets.

See the full article here .

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From Optics & Photonics: “A Topological Shield for Entangled Photons”

From Optics & Photonics

08 November 2018
Stewart Wills

Some researchers in quantum computing look to pairs or ensembles of entangled photons as the best candidates for information-carrying quantum bits (qubits). But entangled photonic quantum states are skittish things, prone to evaporate in imperfect, real-world devices built to meaningful scale. How can the quantum information in photonic qubits be protected long enough to do useful work in a real quantum computer?

Andrea Blanco-Redondo of the University of Sydney Nano Institute led research exploring topological protection for correlated biphoton states, which could clear one hurdle for photons as quantum information carriers. [Image: Jayne Ion/University of Sydney]

One answer could lie in the emerging discipline of topological photonics. A group of researchers in Australia and Israel, led by OSA member Andrea Blanco-Redondo of the University of Sydney Nano Institute, has now experimentally demonstrated a platform for extending “topological protection” to delicate correlated biphoton states—and shown how the platform might be used to build robust logic gates for quantum computing (Science).

Sensitive to imperfections

One of the attractions of photons as qubit candidates is that they are largely immune to the thermal and electromagnetic noise that can bedevil other quantum systems, such as trapped-ion and superconductor platforms. But photonic qubits have their own vulnerabilities. Notably, they’re prone to potential losses and other errors due to scattering as the photons run up against fabrication imperfections.

Thus, while photons have excelled in the lab in proof-of-principle demonstrations of entanglement, it’s been hard to envision how they might be made to work in a practical quantum device, where at least some fabrication defects are unavoidable. Increasingly, however, the physics of topology—which captured the 2016 Nobel Prize for its pioneers in condensed-matter physics—has seemed to hold one key to solving this photonic-qubit quandary.

Protection in topology

One recent example of a topological photonic system, published in February 2018, was a topological-insulator laser demonstrated by a team at The Technion and CREOL. [Image: S. Wittek (CREOL) and M.A. Bandres (Technion)]

Topological systems involve materials that, by virtue of the details of their underlying symmetry, possess unusual physical characteristics, best exemplified by so-called topological edge states. In the realm of photonics, these edge states have been leveraged to create exotic proof-of-principle quantum devices such as chips that steer single photons around corners, and lasers that send light in one direction around the edges of an array of microresonators.

Another key feature stoking interest in “topologically nontrivial” photonic systems is that they are “robust to disorder.” For example, a topological-insulator laser confronting a material defect simply detours around it, and then happily continues on its way around the device perimeter.

That has raised the prospect that this shroud of topological protection could be thrown around single and entangled photons in quantum computers and devices, to keep them safe from losing information to scattering and fabrication imperfections. But experiments thus far in topological protection of photons have generally involved only single photons—not the entangled photon pairs or ensembles required for quantum information systems.

Silicon nanowire array

To extend topological protection to a multiphoton quantum state, Blanco-Redondo’s team—which also included Bryn Bell and OSA Fellow Ben Eggleton at the University of Sydney, and Dikla Oren and OSA Fellow Mordechai Segev at The Technion, Israel—began with a platform that, in previous work [Physical Review Letters], they had shown could produce a topological edge state.

The platform consists of a 1-D array of silicon nanowires with alternating short and long gaps, which creates a structure known as a Su-Schrieffer-Heeger (SSH) lattice. By introducing a “long-long” defect in the middle of the lattice, the team coaxed the structure into displaying topological edge-state behavior and topological protection at the interface between the two-sides of the lattice.

The team’s experimental setup involves a lattice of silicon nanowires with a central defect, which creates an “edge state” that provides topological protection for paired photons traveling down the central waveguide. [Image: Rhys Holland & Sebastian Zentilomo/University of Sydney]

The researchers next pumped light from a picosecond 1550-nm pulsed laser into the waveguide at the center of the lattice. The pump pulses generated correlated signal and idler photons via a spontaneous four-wave mixing (SFWM) process; those photons were filtered, collected in superconducting single-photon detectors, and analyzed at the end of the line to establish correlation between the photons’ quantum states.

Testing for topological protection

Artists’ rendering of correlated photons in the nanowire lattice. [Image: Sebastian Zentilomo/University of Sydney]

Finally, with the presence of correlated biphotons established, the team got down to testing whether the system could provide topological protection for the quantum states of those photon pairs. To do so, the researchers introduced random disorders into the SSH lattice and tested whether the quantum states of the biphotons were preserved.

They found that the correlation and quantum state of the biphotons—which would have been scattered and lost across a uniform, topologically trivial lattice—held up well even amid fairly high levels of lattice disorder in the SSH system. The researchers also demonstrated experimentally how several of these lattices, put together, could form “a key building block” to construct entangled quantum systems with topological protection. And they showed how such entangled systems might be used to create a simple two-qubit logic gate for quantum computing.

Toward photonic quantum gates

Blanco-Redondo, in a press release [no link provided] accompanying the work, suggested that the study results offer “a pathway to build robust entangled states for logic gates using protected pairs of photons.” The team is now working on improving the platform, toward the goal of building such quantum gates. The effort, if successful, could provide a boost to the prospects for photons as quantum information carriers in real-world applications.

See the full article here .

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From Symmetry: “Looking for dark matter using quantum technology”

From Symmetry

10/16/18
Jim Daley

Photo by Reidar Hahn, Fermilab

For decades, physicists have been searching for dark matter, which doesn’t emit light but appears to make up the vast majority of matter in the universe. Several theoretical particles have been proposed as dark matter candidates, including weakly interacting massive particles—called WIMPs—and axions.

Fermilab’s Aaron Chou is leading a multi-institutional consortium to apply the techniques of quantum metrology to the problem of detecting axion dark matter. The project, which brings together scientists at Fermilab, the National Institute of Standards and Technology, the University of Chicago, University of Colorado and Yale University, was recently awarded $2.1 million over two years through the Department of Energy’s Quantum Information Science-Enabled Discovery (QuantISED) program, which seeks to advance science through quantum-based technologies.

If the scientists succeed, the discovery could solve several cosmological mysteries at once.

“It’d be the first time that anybody had found any direct evidence of the existence of dark matter,” says Fermilab’s Daniel Bowring, whose work on this effort is supported by a DOE Office of Science Early Career Research Award. “Right now, we’re inferring the existence of dark matter from the behavior of astrophysical bodies. There’s very good evidence for the existence of dark matter based on those observations, but nobody’s found a particle yet.”

The axion search

Finding an axion would also resolve a discrepancy in particle physics called the strong CP problem. Particles and antiparticles are “symmetrical” to one another: They exhibit mirror-image behavior in terms of electrical charge and other properties.

The strong force—one of the four fundamental forces of nature—obeys CP symmetry. But there’s no reason, at least in the Standard Model of physics, why it should. The axion was first proposed to explain why it does.

Finding an axion is a delicate endeavor, even compared to other searches for dark matter. An axion’s mass is vanishingly low—somewhere between a millionth and a thousandth of an electronvolt. By comparison, the mass of a WIMP is expected to be between a trillion and quadrillion times more massive—in the range of a billion electronvolts—which means they’re heavy enough that they could occasionally produce a signal by bumping into the nuclei of other atoms. To look for WIMPs, scientists fill detectors with liquid xenon (for example, in the LUX-ZEPLIN dark matter experiment at Sanford Underground Research Facility in South Dakota) or germanium crystals (in the SuperCDMS Soudan experiment in Minnesota [not current, now at SNOLAB a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario]) and look for indications of such a collision.

LBNL Lux Zeplin project at SURF

UC Santa Barbara postdoctoral scientist Sally Shaw stands with one of the four large acrylic tanks fabricated for the LZ dark matter experiment’s outer detector.

LZ Dark Matter Experiment at SURF lab

SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

SLAC SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

“You can’t do that with axions because they’re so light,” Bowring says. “So the way that we look for axions is fundamentally different from the way we look for more massive particles.”

When an axion encounters a strong magnetic field, it should—at least in theory—produce a single microwave-frequency photon, a particle of light. By detecting that photon, scientists should be able to confirm the existence of axions. The Axion Dark Matter eXperiment, ADMX, at the University of Washington and the HAYSTAC experiment at Yale are attempting to do just that.

ADMX Axion Dark Matter Experiment at the University of Washington

Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington

U Washington ADMX

Yale HAYSTAC axion dark matter experiment

Yale Haloscope Sensitive To Axion CDM -HAYSTAC Experiment a microwave cavity search for cold dark matter (CDM)

Those experiments use a strong superconducting magnet to convert axions into photons in a microwave cavity. The cavity can be tuned to different resonant frequencies to boost the interaction between the photon field and the axions. A microwave receiver then detects the signal of photons resulting from the interaction. The signal is fed through an amplifier, and scientists look for that amplified signal.

“But there is a fundamental quantum limit to how good an amplifier can be,” Bowring says.

Photons are ubiquitous, which introduces a high degree of noise that must be filtered from the signal detected in the microwave cavity. And at higher resonant frequencies, the signal-to-noise ratio gets progressively worse.

Both Bowring and Chou are exploring how to use technology developed for quantum computing and information processing to get around this problem. Instead of amplifying the signal and sorting it from the noise, they aim to develop new kinds of axion detectors that will count photons very precisely—with qubits.

Aaron Chou works on an FNAL experiment that uses qubits to look for direct evidence of dark matter in the form of axions. Photo by Reidar Hahn, Fermilab

The qubit advantage

In a quantum computer, information is stored in qubits, or quantum bits.

Quantum computing – IBM

A qubit can be constructed from a single subatomic particle, like an electron or a photon, or from engineered metamaterials such as superconducting artificial atoms. The computer’s design takes advantage of the particles’ two-state quantum systems, such as an electron’s spin (up or down) or a photon’s polarization (vertical or horizontal). And unlike classical computer bits, which have one of only two states (one or zero), qubits can also exist in a quantum superposition, a kind of addition of the particle’s two quantum states. This feature has myriad potential applications in quantum computing that physicists are just starting to explore.

In the search for axions, Bowring and Chou are using qubits. For a traditional antenna-based detector to notice a photon produced by an axion, it must absorb the photon, destroying it in the process. A qubit, on the other hand, can interact with the photon many times without annihilating it. Because of this, the qubit-based detector will give the scientists a much higher chance of spotting dark matter.

“The reason we want to use quantum technology is that the quantum computing community has already had to develop these devices that can manipulate a single microwave photon,” Chou says. “We’re kind of doing the same thing, except a single photon of information that’s stored inside this container is not something that somebody put in there as part of the computation. It’s something that the dark matter put in there.”

Light reflection

Using a qubit to detect an axion-produced photon brings its own set of challenges to the project. In many quantum computers, qubits are stored in cavities made of superconducting materials. The superconductor has highly reflective walls that effectively trap a photon long enough to perform computations with it. But you can’t use a superconductor around high-powered magnets like the ones used in Bowring and Chou’s experiments.

“The superconductor is just ruined by magnets,” Chou says. Currently, they’re using copper as an ersatz reflector.

“But the problem is, at these frequencies the copper will store a single photon for only 10,000 bounces instead of, say, a billion bounces off the mirrors,” he says. “So we don’t get to keep these photons around for quite as long before they get absorbed.”

And that means that they don’t stick around long enough to be picked up as a signal. So the researchers are developing another, better photon container.

“We’re trying to make a cavity out of very low-loss crystals,” Chou says.

Think of a windowpane. As light hits it, some photons will bounce off it, and others will pass through. Place another piece of glass behind the first. Some of the photons that passed through the first will bounce off the second, and others will pass through both pieces of glass. Add a third layer of glass, and a fourth, and so on.

“Even though each individual layer is not that reflective by itself, the sum of the reflections from all the layers gives you a pretty good reflection in the end,” Chou says. “We want to make a material that traps light for a long time.”

Bowring sees the use of quantum computing technology in the search for dark matter as an opportunity to reach across the boundaries that often keep different disciplines apart.

“You might ask why Fermilab would want to get involved in quantum technology if it’s a particle physics laboratory,” he says. “The answer is, at least in part, that quantum technology lets us do particle physics better. It makes sense to lower those barriers.”

See the full article here .

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Symmetry is a joint Fermilab/SLAC publication.

From UC Davis egghead blog: “Grants for Quantum Information Science”

From UC Davis egghead blog

UC Davis egghead blog

October 9th, 2018
Andy Fell

The QMAP initiative at UC Davis is aimed at fundamental research in theoretical and mathematical physics.

The U.S. Department of Energy recently announced $218 million in new grants for “Quantum Information Science” and researchers with the Center for Quantum Mathematics and Physics (QMAP) at UC Davis are among the recipients.

Professors Veronika Hubeny and Mukund Rangamani were awarded $348,000 over two years for work on “Entanglement in String Theory and the Emergence of Geometry.” They will explore connections between the nature of spacetime, quantum entanglement and string theory. Entanglement, famously described by Einstein as “spooky action at a distance,” is a phenomenon in quantum physics where the properties of pairs of particles are correlated even when they are widely separated.

Another grant in the program went to a team including Professor Andreas Albrecht and led by Andrew Sornborger, scientist at the Los Alamos National Laboratory and a research associate in the UC Davis Department of Mathematics. They will work on “Disentangling Quantum Entanglement: A Machine Learning Approach to Decoherence, Quantum Error Correction, and Phase Transition Dynamics.” This research will involve investigating quantum theories with a variety of model systems, including using machine learning to interpret and understand the models. The larger goals are understanding the emergence of locality and the arrow of time in the physics that governs the cosmos, Albrecht said.

The energy department’s program is a long-term investment in research towards the next generation of computing and information technologies, according to their news release. While digital computers are based on “bits” that are ones or zeroes, a quantum computer work with “qubits” that exploit the properties of quantum theory – such as entanglement – to function.

Working quantum computers are in their very early infancy, but they could theoretically achieve tasks that are not possible or too time-consuming for current computing technology.

Quantum computing – IBM

The grants awarded range from new materials, hardware and software to the implications of quantum computing for fundamental physics.

QMAP was founded in 2015 in the College of Letters and Science with the goal of having mathematicians and physicists work together on topics at the intersection of both fields such as quantum gravity, quantum field theory and string theory. Albrecht is the center’s founding director; Hubeny and Rangamani are among the first faculty hired for the center.

See the full article here .

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About Egghead

Egghead is a blog about research by, with or related to UC Davis. Comments on posts are welcome, as are tips and suggestions for posts. General feedback may be sent to Andy Fell. This blog is created and maintained by UC Davis Strategic Communications, and mostly edited by Andy Fell.

The University of California, Davis, is a major public research university located in Davis, California, just west of Sacramento. It encompasses 5,300 acres of land, making it the second largest UC campus in terms of land ownership, after UC Merced.

From Caltech: “Superconducting Metamaterial Traps Quantum Light”

From Caltech

09/26/2018

Robert Perkins
(626) 395-1862
rperkins@caltech.edu

A superconducting metamaterial chip mounted into a microwave test package. The purplish-violet reflection in the center is an optical effect that can seen by the naked eye, and is the result of the diffaction of light by the periodic patterning of the microwave metamaterial. Credit: Oskar Painter/Caltech

Newly developed material may be key to scaling up quantum circuits.

Conventional computers store information in a bit, a fundamental unit of logic that can take a value of 0 or 1. Quantum computers rely on quantum bits, also known as a “qubits,” as their fundamental building blocks. Bits in traditional computers encode a single value, either a 0 or a 1. The state of a qubit, by contrast, can simultaneously have a value of both 0 and 1. This peculiar property, a consequence of the fundamental laws of quantum physics, results in the dramatic complexity in quantum systems.

Quantum computing is a nascent and rapidly developing field that promises to use this complexity to solve problems that are difficult to tackle with conventional computers. A key challenge for quantum computing, however, is that it requires making large numbers of qubits work together—which is difficult to accomplish while avoiding interactions with the outside environment that would rob the qubits of their quantum properties.

New research from the lab of Oskar Painter, John G Braun Professor of Applied Physics and Physics in the Division of Engineering and Applied Science, explores the use of superconducting metamaterials to overcome this challenge.

Metamaterials are specially engineered by combining multiple component materials at a scale smaller than the wavelength of light, giving them the ability to manipulate how particles of light, or photons, behave. Metamaterials can be used to reflect, turn, or focus beams of light in nearly any desired manner. A metamaterial can also create a frequency band where the propagation of photons becomes entirely forbidden, a so-called “photonic bandgap.”

The Caltech team used a photonic bandgap to trap microwave photons in a superconducting quantum circuit, creating a promising technology for building future quantum computers.

“In principle, this is a scalable and flexible substrate on which to build complex circuits for interconnecting certain types of qubits,” says Painter, leader of the group that conducted the research, which was published in Nature Communications on September 12. “Not only can one play with the spatial arrangement of the connectivity between qubits, but one can also design the connectivity to occur only at certain desired frequencies.”

Painter and his team created a quantum circuit consisting of thin films of a superconductor—a material that transmits electric current with little to no loss of energy—traced onto a silicon microchip. These superconducting patterns transport microwaves from one part of the microchip to another. What makes the system operate in a quantum regime, however, is the use of a so-called Josephson junction, which consists of an atomically thin non-conductive layer sandwiched between two superconducting electrodes. The Josephson junction creates a source of microwave photons with two distinct and isolated states, like an atom’s ground and excited electronic states, that are involved in the emission of light, or, in the language of quantum computing, a qubit.

“Superconducting quantum circuits allow one to perform fundamental quantum electrodynamics experiments using a microwave electrical circuit that looks like it could have been yanked directly from your cell phone,” Painter says. “We believe that augmenting these circuits with superconducting metamaterials may enable future quantum computing technologies and further the study of more complex quantum systems that lie beyond our capability to model using even the most powerful classical computer simulations.”

The paper is titled “Superconducting metamaterials for waveguide quantum electrodynamics,” The team of authors was led by Mohammad Mirhosseini, a Kavli Nanoscience Institute Postdoctoral Scholar at Caltech. Co-authors include postdoctoral scholars Andrew Keller and Alp Sipahigil of the Institute for Quantum Information and Matter (IQIM); and graduate students Eun Jong Kim, Vinicius Ferreira, and Mahmoud Kalaee. The work was performed as part of a pair of Multidisciplinary University Research Initiatives from the Air Force Office of Scientific Research (“Quantum Photonic Matter” and “Wiring Quantum Networks with Mechanical Transducers”), and in conjunction with IQIM, a National Science Foundation Physics Frontiers Center supported by the Gordon and Betty Moore Foundation.

See the full article here .

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The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

Caltech campus

From UC Santa Cruz: “Quantum information science on the verge of a technological revolution” Revised

From UC Santa Cruz

September 13, 2018
Tim Stephens
stephens@ucsc.edu

Theorist Yuan Ping is developing computational methods to guide the design of new materials for quantum computing and other quantum information technologies.

Materials scientist Yuan Ping (center) with graduate student Tyler Smart (left) and postdoctoral fellow Feng Wu (right) at the UCSC supercomputer center. (Photo by C. Lagattuta)

See https://sciencesprings.wordpress.com/2018/09/10/from-uc-santa-cruz-nsf-funds-powerful-new-supercomputer-for-uc-santa-cruz-researchers/

Researchers are racing to develop quantum information technologies, in which information will be stored in quantum bits, or qubits. Qubits can be made from any quantum system that has two states, such as the spin states of electrons. (Image credit: National Science Foundation)

Quantum computers may one day solve problems that are effectively beyond the capacity of conventional supercomputers. Quantum communications may enable instantaneous, secure transmission of information across vast distances, and quantum sensors may provide previously unheard of sensitivities.

A global race is on to develop these new quantum information technologies, in which information will be stored in quantum bits, or qubits. In conventional digital technologies, a bit is either 0 or 1, whereas a qubit can represent both states at the same time because of a strange phenomenon of quantum physics called superposition. In theory, this will enable a massive increase in computing speed and capacity for certain types of calculations.

At UC Santa Cruz, materials scientists are working to develop novel materials that can serve as the foundation for quantum information technology, just as silicon chips paved the way for today’s digital technologies. Several different systems for creating and manipulating qubits have been proposed and implemented, but for now they remain too cumbersome for real-world applications.

“Our focus as materials scientists is on what material we should use as the fundamental element to carry the information. Other researchers are more concerned with how to wire it up to make a device that can perform calculations, but we’re focused on the material basis of the qubit,” said Yuan Ping, assistant professor of chemistry and biochemistry at UC Santa Cruz.

2D materials

In particular, Ping and other UCSC researchers are focusing on defects in extremely thin materials, called two-dimensional (2D) materials. Defects or imperfections in the atomic structure of a material can function as qubits because information can be encoded in the spin states of their electrons. This phenomenon has been well studied in other types of materials, most notably the “nitrogen vacancy” or NV defect in diamond. But according to Ping, 2D materials offer significant advantages.

“Unlike diamond, 2D materials are relatively cheap and easy to make, they are scalable, and they are easy to integrate into a solid-state device,” she said. “They are also stable at room temperature, which is important because a lot of the qubit systems implemented so far use superconductors that can only operate at very low temperatures.”

There are a lot of different 2D materials, however, and a lot of ways to put defects into them. The possibilities are almost endless, and it’s not practical to synthesize and test them all experimentally to see which have the best properties for quantum technologies.

That’s where theorists like Ping come in. She is developing computational methods that can be used to predict the properties of defects in 2D materials reliably and efficiently. In December 2017, her team published a paper in Physical Review Materials establishing the fundamental principles for doing calculations to accurately describe charge defects, electronic states, and spin dynamics in 2D materials. (Her coauthors on the paper include postdoctoral fellow Feng Wu, graduate student Andrew Galatas, and collaborators Dario Rocca at University of Lorraine in France and Ravishankar Sundararaman at Rensselaer Polytechnic Institute.)

In July, Ping won a $350,000 grant from the National Science Foundation to further develop these computational methods.

“We’re developing a reliable set of tools to predict the electronic structure, excited-state lifetime, and quantum-state coherence time of defects in 2D materials at a quantum mechanical level,” Ping said. “We do calculations from first principles, meaning we don’t need any input from experiments. Everything is predicted based on quantum mechanics.”

Quantum weirdness

The world of quantum mechanics is notoriously counter-intuitive and hard to grasp. Concepts such as superposition and entanglement defy common sense, yet they have been demonstrated conclusively and are fundamental to quantum information technologies. Superposition, when a particle exists in two different states simultaneously, is often compared to a spinning coin, neither heads nor tails until it stops spinning. Entanglement creates a link between the quantum states of two particles or qubits, so it is as if the outcome of one spinning coin determined the outcome of another spinning coin.

A major challenge in exploiting these phenomena for quantum information technologies is their inherent fragility. Interaction with the environment causes a superposition to fall into one state or the other. Called decoherence, this can be caused by vibrations of the atoms in the material and other subtle effects.

“You want qubits to be well insulated from the environment to give longer coherence times,” Ping said.

One 2D material that has shown promise for quantum technologies is ultrathin hexagonal boron nitride. Ping used her computational methods to investigate various defects in this material and identified a promising candidate for scalable quantum applications. This defect (a nitrogen vacancy adjacent to carbon substitution of boron) is predicted to have stable spin states well insulated from the environment and bright optical transitions, making it a good source for single photon emission and a good candidate for qubits.

“Quantum emitters, which can emit one photon at a time, are important for optically-based quantum information processing, information security, and ultrasensitive sensing,” Ping said.

She works closely with experimentalists, helping to interpret their results and guide their efforts to create novel materials with desirable properties for quantum technologies. Her group is part of a large collaborative effort, the Quantum Information Science and Engineering Network (QISE-NET), funded by the National Science Foundation. Tyler Smart, a graduate student in Ping’s group, is funded by QISE-NET and is working on a project at Argonne National Laboratory.

“He will be traveling to Chicago to present his research every few months,” Ping said. “There are about 20 universities as well as national laboratories and industry partners in the network, meeting regularly and sharing ideas, which is important because it’s a fast-moving field.”

One of the National Science Foundation’s 10 Big Ideas for Future NSF Investments is “The Quantum Leap: Leading the Next Quantum Revolution.”

The Department of Energy is also investing in this area, as are companies such as Google and Intel, hoping to exploit quantum mechanics to develop next-generation technologies for computing, sensing, and communications.

“They are all investing in it because it will take a lot of effort to develop this field, and the potential is so great,” Ping said.

See the full article here .

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Shane Telescope at UCO Lick Observatory, UCSC

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

UCSC is the home base for the Lick Observatory.

Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

Search for extraterrestrial intelligence expands at Lick Observatory
New instrument scans the sky for pulses of infrared light
March 23, 2015
By Hilary Lebow

The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

“Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

“The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

“We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

“This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

“Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

From Yale University via Science Alert: “For The First Time, Scientists Have Teleported And Measured a Quantum Gate in Real Time”

From Yale University

via

Science Alert

6 SEP 2018
MIKE MCRAE

(agsandrew/istock)

Welcome to the future.

Around 20 years ago, two computer scientists proposed a technique for teleporting a special quantum operation between two locations with the goal of making quantum computers more reliable.

Now a team of researchers from Yale University have successfully turned their idea into reality, demonstrating a practical approach to making this incredibly delicate form of technology scalable.

These physicists have developed a practical method for teleporting a quantum operation – or gate – across a distance and measuring its effect. While this feat has been done before, it’s never been done in real time. This paves the way for developing a process that can make quantum computing modular, and therefore more reliable.

Unlike regular computers, which perform their calculations with states of reality called bits (on or off, 1 or 0), quantum computers operate with qubits – a strange state of reality we can’t wrap our heads around, but which taps into some incredibly useful mathematics.

In classical computers, bits interact with operations called logic gates. Like the world’s smallest gladiatorial arena, two bits enter, one bit leaves. Gates come in different forms, selecting a winner depending on their particular rule.

These bits, channelled through gates, form the basis of just about any calculation you can think of, as far as classical computers are concerned.

But qubits offer an alternative unit to base algorithms on. More than just a 1 or a 0, they also provide a special blend of the two states. It’s like a coin held in a hand before you see whether it’s heads or tails.

In conjunction with a quantum version of a logic gate, qubits can do what classical bits can’t. There’s just one problem – that indeterminate state of 1 and 0 turns into a definite 1 or 0 when it becomes part of a measured system.

Worse still, it doesn’t take much to collapse the qubit’s maybe into a definitely, which means a quantum computer can become an expensive paperweight if those delicate components aren’t adequately hidden from their noisy environment.

Right now, quantum computer engineers are super excited by devices that can wrangle just over 70 qubits – which is impressive, but quantum computers will really only earn their keep as they stock up on hundreds, if not thousands of qubits all hovering on the brink of reality at the same time.

To make this kind of scaling a reality, scientists need additional tricks. One option would be to make the technology as modular as possible, networking smaller quantum systems into a bigger one in order to offset errors.

But for that to work, quantum gates – those special operations that deal with the heavy lifting of qubits – also need to be shared.

Teleporting information, such as a quantum gate, sounds pretty sci-fi. But we’re obviously not talking about Star Trek transport systems here.

In reality it simply refers to the fact that objects can have their history entangled so that when one is measured, the other immediately collapses into a related state, no matter how far away it is.

This has technically been demonstrated experimentally already [Physical Review Letters], but, until now, the process hasn’t been reliably performed and measured in real time, which is crucial if it’s to become part of a practical computer.

“Our work is the first time that this protocol has been demonstrated where the classical communication occurs in real-time, allowing us to implement a ‘deterministic’ operation that performs the desired operation every time,” says lead author Kevin Chou.

The researchers used qubits in sapphire chips inside a cutting-edge setup to teleport a type of quantum operation called a controlled-NOT gate. Importantly, by applying error-correctable coding, the process was 79 percent reliable.

“It is a milestone toward quantum information processing using error-correctable qubits,” says principal investigator Robert Schoelkopf.

It’s a baby step on the road to making quantum modules, but this proof-of-concept shows modules could still be the way to go in growing quantum computers to the scale we need.

This research was published in Nature.

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.