What is the recent achievement in photonics-based quantum computing that is reported in Nature Photonics?

Researchers in nuclear physics and quantum information have achieved a significant breakthrough by using a photon-number-resolving system to accurately detect over 100 photons. This advancement marks a major step forward in quantum computing development and could potentially enable the generation of truly random numbers, a critical component for developing unbreakable encryption techniques used in military communications and financial transactions. The team reported their findings in Nature Photonics.

Scientists worldwide are fervently pursuing the promise of reliable and robust quantum computing, which could bring significant advancements in science, economics, and national security. However, achieving this goal has proven challenging for even the most brilliant minds.

A pair of engineers from the US Department of Energy’s Thomas Jefferson National Accelerator Facility have designed a critical component of a photon detection system that brings physicists one step closer to developing a fully operational photonics-based quantum computer, constructed entirely with light. These engineers are part of an interdisciplinary team of researchers from both the government and academia led by Jefferson Lab, working to advance nuclear physics-based quantum computing.

There are numerous approaches to developing a fully functional quantum computer, and for photonics-based computing, accurately detecting photons is crucial. Currently, individual detectors can only detect up to 10 photons, which is insufficient for many quantum-state generation methods. Although no one has yet demonstrated the detection of more than 16 photons, simulations suggest that quantum computing will require the detection of large numbers of photons, likely exceeding 50.

The achievement of detecting over 50 photons is a critical milestone in developing a complete gate set for universal quantum computing. The team, led by Amr Hossameldin, a graduate research assistant in quantum computing and quantum optics at the University of Virginia, surpassed the previous record of 16 photons. Using a photon-number-resolving system, they were able to detect 35 photons per single detector and 100 photons with a three-detector system, achieving an unprecedented level of accuracy.

Robert Edwards, senior staff scientist and deputy associate director for theoretical and computational physics at Jefferson Lab, explained that the lack of photon detection has been a significant limitation in quantum computing, but the team’s breakthrough is a necessary step toward implementing a universal instruction set.

In addition to advancing quantum computing, the team’s new detection system has a secondary benefit: quantum generation of truly random numbers. Unlike random numbers generated by classical computer algorithms, which can be compromised, true random-number generation using quantum physics has no bias and is essential in developing unbreakable encryption techniques used in areas like military communications and financial transactions.

Olivier Pfister, a physics professor at UVa who specializes in quantum fields and quantum information, and who served as the external team leader for the project, explained that quantum mechanics has an intrinsic randomness, making it impossible to predict which physical state a system is in. This unpredictability is what makes quantum-generated random numbers truly random and impossible to compromise.

The team’s research was presented in a paper co-authored by Pfister, Hossameldin, Chris Cuevas, and Hai Dong from Jefferson Lab, Richard Birrittella and Paul Alsing from the Air Force Research Laboratory in New York, Miller Eaton from UVa, and Christopher C. Gerry from the City University of New York.

Signals not seen before

The team’s project was initiated after the DOE Office of Science announced funding opportunities for quantum information science research for nuclear physics in 2019 under the Quantum Horizons program. Edwards was able to secure a small grant to fund a lecture series that brought in experts in quantum computing.

Pfister was the first lecturer in March 2020, but the lab was shut down due to the COVID-19 pandemic a week later. However, the idea for joint research into photonics-based quantum computing had already been planted.

The team comprised a large group of physicists, engineers, and postdocs. They initially aimed to use quantum photonics to make calculations relevant to the Jefferson Lab science program.

UVa had a photon-based system for quantum calculations using a pulsed laser, but lacked the ability to detect the number of photons impacting on its detector with great speed and accuracy before the signal decayed.

On the other hand, Jefferson Lab’s forte was detecting particles with speed and accuracy. Its CEBAF facility has been used for decades in experiments that rely on ultra-sensitive detectors to measure the cascade of fleeting subatomic particles created when a particle beam slams into targets at nearly the speed of light.

In a team experiment at UVa’s Quantum Optics Lab, Hossameldin used three superconducting transition-edge sensor (TES) devices to make one detector, with each TES device capable of seeing 35 photons, and placed them in front of the laser beam. Dong’s high-speed digitizer was a crucial component of the detector electronics.

Cuevas noted that the team’s system will likely be replaced by new technology soon, given the exponential pace of quantum computing research. However, the collaboration to build a light-based quantum computer will continue, and Cuevas believes that sharing technology is a core foundation for the scientific communities.

Source: Thomas Jefferson National Accelerator Facility

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