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Primeur weekly 2019-05-20

Quantum computing

D-Wave makes new lower-noise quantum processor available in Leap ...

Atos delivers world's highest-performing quantum simulator to multinational energy company Total ...

Digital quantum simulators can be astonishingly robust ...

Generating high-quality single photons for quantum computing ...

Quantum world-first: researchers reveal accuracy of two-qubit calculations in silicon ...

Accelerating quantum technologies with materials processing at the atomic scale ...

Focus on Europe

GCS grants more than 1 billion computing core hours to national large-scale research projects ...

GCS announces new Chair of the Board, Prof. Dr. Dieter Kranzlmüller ...

Applications to 19th PRACE Project Access Call ...

PRACE Awards @ EuroHPC Summit Week 2019 ...

ISC High Performance announce David Keyes as 2020 Programme Chair ...

National eScience Symposium 2019 to cover Digital Challenges in Open Science ...

Middleware

RedLine becomes Bright Computing Services Partner ...

eSilicon chooses Univa to manage complex ASIC chip designs for high-bandwidth networking, high-performance computing, AI and 5G infrastructure applications ...

Hardware

Boston Limited to officially launch operations in South Africa during a series of High-Performance Computing (HPC) events hosted by the Centre for High-Performance Computing (CHPC) ...

HPE to acquire supercomputing vendor Cray ...

China to build new national supercomputing centre ...

Mellanox Capital invests in storage experts Excelero and WekaIO ...

Mellanox introduces advanced Network Telemetry technology to keep your business up and running ...

Supermicro announces third quarter fiscal 2019 preliminary financial information and files 2017 form 10-K and form 10-Q/As ...

Atos launches the world's highest performing Edge Computing server ...

NVIDIA announces financial results for first quarter fiscal 2020 ...

NERSC's Edison supercomputer to retire after five years of service ...

WekaIO raises $31,7 million in Series C funding ...

Energy free superfast computing invented by scientists using light pulses ...

Applications

Atos launches myQLM to democratize quantum programming for researchers, students and developers worldwide ...

A step towards probabilistic computing ...

CosmoGAN: Training a neural network to study dark matter ...

New AI sees like a human, filling in the blanks ...

Generating high-quality single photons for quantum computing

14 May 2019 Cambridge - MIT researchers have designed a way to generate, at room temperature, more single photons for carrying quantum information. The design, they say, holds promise for the development of practical quantum computers.

Quantum emitters generate photons that can be detected one at a time. Consumer quantum computers and devices could potentially leverage certain properties of those photons as quantum bits ("qubits") to execute computations. While classical computers process and store information in bits of either 0s or 1s, qubits can be 0 and 1 simultaneously. That means quantum computers could potentially solve problems that are intractable for classical computers.

A key challenge, however, is producing single photons with identical quantum properties - known as "indistinguishable" photons. To improve the indistinguishability, emitters funnel light through an optical cavity where the photons bounce back and forth, a process that helps match their properties to the cavity. Generally, the longer photons stay in the cavity, the more they match.

But there's also a trade-off. In large cavities, quantum emitters generate photons spontaneously, resulting in only a small fraction of photons staying in the cavity, making the process inefficient. Smaller cavities extract higher percentages of photons, but the photons are lower quality, or "distinguishable".

In a paper published in Physical Review Letters , the researchers split one cavity into two, each with a designated task. A smaller cavity handles the efficient extraction of photons, while an attached large cavity stores them a bit longer to boost indistinguishability.

Compared to a single cavity, the researchers' coupled cavity generated photons with around 95 percent indistinguishability, compared to 80 percent indistinguishability, with around three times higher efficiency.

"In short, two is better than one", stated first author Hyeongrak "Chuck" Choi, a graduate student in the MIT Research Laboratory of Electronics (RLE). "What we found is that in this architecture, we can separate the roles of the two cavities: The first cavity merely focuses on collecting photons for high efficiency, while the second focuses on indistinguishability in a single channel. One cavity playing both roles can't meet both metrics, but two cavities achieves both simultaneously."

Joining Hyeongrak "Chuck" Choi on the paper are: Dirk Englund, an associate professor of electrical engineering and computer science, a researcher in RLE, and head of the Quantum Photonics Laboratory; Di Zhu, a graduate student in RLE; and Yoseob Yoon, a graduate student in the Department of Chemistry.

The relatively new quantum emitters, known as "single-photon emitters", are created by defects in otherwise pure materials, such as diamonds, doped carbon nanotubes, or quantum dots. Light produced from these "artificial atoms" is captured by a tiny optical cavity in photonic crystal - a nanostructure acting as a mirror. Some photons escape, but others bounce around the cavity, which forces the photons to have the same quantum properties - mainly, various frequency properties. When they're measured to match, they exit the cavity through a waveguide.

But single-photon emitters also experience tons of environmental noise, such as lattice vibrations or electric charge fluctuation, that produce different wavelength or phase. Photons with different properties cannot be "interfered", such that their waves overlap, resulting in interference patterns. That interference pattern is basically what a quantum computer observes and measures to do computational tasks.

Photon indistinguishability is a measure of photons' potential to interfere. In that way, it's a valuable metric to simulate their usage for practical quantum computing. "Even before photon interference, with indistinguishability, we can specify the ability for the photons to interfere", Hyeongrak "Chuck" Choi stated. "If we know that ability, we can calculate what's going to happen if they are using it for quantum technologies, such as quantum computers, communications, or repeaters."

In the researchers' system, a small cavity sits attached to an emitter, which in their studies was an optical defect in a diamond, called a "silicon-vacancy centre" - a silicon atom replacing two carbon atoms in a diamond lattice. Light produced by the defect is collected into the first cavity. Because of its light-focusing structure, photons are extracted with very high rates. Then, the nanocavity channels the photons into a second, larger cavity. There, the photons bounce back and forth for a certain period of time. When they reach a high indistinguishability, the photons exit through a partial mirror formed by holes connecting the cavity to a waveguide.

Importantly, Hyeongrak "Chuck" Choi said, neither cavity has to meet rigorous design requirements for efficiency or indistinguishability as traditional cavities, called the "quality factor" (Q-factor). The higher the Q-factor, the lower the energy loss in optical cavities. But cavities with high Q-factors are technologically challenging to make.

In the study, the researchers' coupled cavity produced higher quality photons than any possible single-cavity system. Even when its Q factor was roughly one-hundredth the quality of the single-cavity system, they could achieve the same indistinguishability with three times higher efficiency.

The cavities can be tuned to optimize for efficiency versus indistinguishability - and to consider any constraints on the Q factor - depending on the application. That's important, Hyeongrak "Chuck" Choi added, because today's emitters that operate at room temperature can vary greatly in quality and properties.

Next, the researchers are testing the ultimate theoretical limit of multiple cavities. One more cavity would still handle the initial extraction efficiently, but then would be linked to multiple cavities that photons for various sizes to achieve some optimal indistinguishability. But there will most likely be a limit, Hyeongrak "Chuck" Choi stated: "With two cavities, there is just one connection, so it can be efficient. But if there are multiple cavities, the multiple connections could make it inefficient. We're now studying the fundamental limit for cavities for use in quantum computing."

Source: Massachusetts Institute of Technology - MIT

Back to Table of contents

Primeur weekly 2019-05-20

Quantum computing

D-Wave makes new lower-noise quantum processor available in Leap ...

Atos delivers world's highest-performing quantum simulator to multinational energy company Total ...

Digital quantum simulators can be astonishingly robust ...

Generating high-quality single photons for quantum computing ...

Quantum world-first: researchers reveal accuracy of two-qubit calculations in silicon ...

Accelerating quantum technologies with materials processing at the atomic scale ...

Focus on Europe

GCS grants more than 1 billion computing core hours to national large-scale research projects ...

GCS announces new Chair of the Board, Prof. Dr. Dieter Kranzlmüller ...

Applications to 19th PRACE Project Access Call ...

PRACE Awards @ EuroHPC Summit Week 2019 ...

ISC High Performance announce David Keyes as 2020 Programme Chair ...

National eScience Symposium 2019 to cover Digital Challenges in Open Science ...

Middleware

RedLine becomes Bright Computing Services Partner ...

eSilicon chooses Univa to manage complex ASIC chip designs for high-bandwidth networking, high-performance computing, AI and 5G infrastructure applications ...

Hardware

Boston Limited to officially launch operations in South Africa during a series of High-Performance Computing (HPC) events hosted by the Centre for High-Performance Computing (CHPC) ...

HPE to acquire supercomputing vendor Cray ...

China to build new national supercomputing centre ...

Mellanox Capital invests in storage experts Excelero and WekaIO ...

Mellanox introduces advanced Network Telemetry technology to keep your business up and running ...

Supermicro announces third quarter fiscal 2019 preliminary financial information and files 2017 form 10-K and form 10-Q/As ...

Atos launches the world's highest performing Edge Computing server ...

NVIDIA announces financial results for first quarter fiscal 2020 ...

NERSC's Edison supercomputer to retire after five years of service ...

WekaIO raises $31,7 million in Series C funding ...

Energy free superfast computing invented by scientists using light pulses ...

Applications

Atos launches myQLM to democratize quantum programming for researchers, students and developers worldwide ...

A step towards probabilistic computing ...

CosmoGAN: Training a neural network to study dark matter ...

New AI sees like a human, filling in the blanks ...