Laser-powered quantum computers need a system that can accurately and reliably count and distinguish individual particles of light, called photons. Currently, individual detectors can count and distinguish as many as approximately 10 photons. However, working quantum computers will need to count 50 or more photons every few nanoseconds. A team designed, built, and tested a photon detection system for this type of quantum computer. In the tests, the new system accurately resolved more than 100 photons every few microseconds. This demonstration proves the feasibility of this type of laser-powered quantum computer.
This test is a major step forward in capability for quantum computers. It also opens the door for implementation of a “cubic phase gate.” This feature would enable more robust and fault-tolerant calculations by quantum computers. Beyond science, quantum computing has the potential to elevate the economy and enhance national security. For instance, random numbers generated by today’s computer algorithms aren’t truly random. They are generated from an algorithm that can be cracked. Quantum generation of truly random numbers makes it possible to generate unbreakable secret codes or encryptions for use in the military and financial sectors.
One option researchers are exploring for quantum computing is a system built entirely on light. Such photonics-based systems require accurate quantum detection of light particles, or photons. Currently, individual prototype detectors for such systems can resolve fewer than 20 photons. Simulations suggest that quantum computing will require detecting 50 photons or more. Crossing that 50-photon threshold means being able to implement a “cubic phase gate,” a milestone toward building a complete gate set for universal quantum computing.
Engineers and physicists from the Thomas Jefferson National Accelerator Facility and the University of Virginia tested a new concept. The team worked with an existing photon-based quantum computer setup. The setup was designed to make quantum calculations using a pulsed laser. The computer’s original photon detector couldn’t count the number of photons being emitted with great speed and accuracy before the signal decayed. The team replaced the original detector with a system that linked up three superconducting transition-edge sensor (TES) devices to make one detector. The team also incorporated a unique, high-speed digitizer. In tests, the three-detector prototype reached 100 photons and featured 12-bit accuracy.
Thomas Jefferson National Accelerator Facility
This material is based on work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics, the National Science Foundation, the National Research Council Research Associate Program, the Air Force Research Laboratory Summer Faculty Fellowship Program, the Air Force Office of Scientific Research, and the Thomas Jefferson National Accelerator Facility Lab Directed Research and Development program.
Eaton, M., et al., Resolution of 100 photons and quantum generation of unbiased random numbers. Nature Photonics 17, 106–111 (2023). [DOI: https://doi.org/10.1038/s41566-022-01105-9]
Counting Photons for Quantum Computing, a Thomas Jefferson National Accelerator Facility feature story