Breakthroughs in Low Light and Long Wavelength Detection Bring Quantum Technology Closer to Realitymkw3a@virginia.edu
A research group at UVA’s Charles L. Brown Department of Electrical and Computer Engineering is pushing the boundaries in quantum information and quantum computing, emerging fields that could revolutionize the discovery of knowledge in the physical and life sciences and take the next leap in cybersecurity.
“It’s a wicked problem, analogous to where the electronics industry stood in the 1950s with breakthroughs in transistors and integrated circuitry,” said Joe Campbell, Lucien Carr III Professor of electrical and computer engineering at UVA.
Many of the proposed architectures for quantum computers and networks rely on photonics, a merger of optics and electronics. Campbell and electrical and computer engineering professors Andreas Beling and Xu Yi formed a multidisciplinary team led by Olivier Pfister, professor of experimental, atomic, molecular and optical physics at UVA, to develop integrated “quantum photonics” on a computer chip.
Just like the computers in use today, quantum computing involves inputs, throughputs and outputs. Pfister’s research group developed the underlying framework to replicate these processes in a quantum state. The key pieces are a quantum emitter, a device that generates photons in pairs, rather than one-by-one as lasers do; a means to tune the emitters and perturb the photons; and a photon detector, which converts the photons into an electrical signal.
Each element—the emitter, tuner and detector—requires its own process of design and fabrication. Yi’s group is developing ultra-stable integrated sources of quantum light. Beling’s group discovered a way to design two chips with interconnecting elements, which when sandwiched together like an Oreo cookie to form a complete and closed-loop circuitry. Beling credits his Ph.D. student Qianhuan Yu for achieving this major milestone. Yu developed the wafer bonding technique to integrate highly efficient light detectors on a silicon nitride platform, which offers low light attenuation and wide transparency.
Advancements in one of the elements boosts the performance of the circuit as a whole. In a recent breakthrough, Campbell’s group developed an avalanche photon detector for low light. Using aluminum indium arsenide antimonide as the material from which the detectors are fabricated, high single photon detection efficiencies have been achieved.
This enhanced capability enables detection of photons with up to two microns wavelength. Standard detectors, based on silicon, are good at detecting photons in the spectral range of less than 0.9 microns. These avalanche photodiodes can operate at the wavelengths employed for fiber optic communications, with detection sensitivity comparable to silicon but at 10 times higher speeds. At longer wavelengths, Campbell speculates that photon detectors tuned to two microns may become the standard for light detection and ranging sensing applications such as unmanned or aerial vehicles.
Supported by grants from the National Science Foundation, the team aims to overcome two more challenges in making quantum technology a reality. One challenge is to achieve scalability. This involves connecting qubits, the basic unit of information for quantum computing, through on-chip interconnects and also fiber optic links. Advancements in scalability could transform how we think of data centers, by connecting quantum computers within a network.
A second challenge is to circumvent decoherence, when a noisy environment quantitatively degrades the quantum performances of the photon detectors. Advancements in decoherence will make receivers more efficient and less error prone by improving the signal-to-noise ratio. Whereas state-of-the-art research has yielded proof-of-principle results in one or the other problem set, the UVA team is uniquely positioned to engineer a device that achieves both scalability and decoherence simultaneously.