Collaborative Research: CIF: FET: Small: Realizing Joint Detection Receivers for Quantum-enhanced Optical Communications using Photonic NISQ-era Quantum Processors

Optical laser communication will constitute a key component of future space-based data communication systems including deep-space communications. It can support significantly higher data rates compared to traditional radio-frequency communication with lower size, weight and transmission power requirements. The ultimate data rates, or in other words, the communication capacity of long-range optical lasercom links, are governed by the laws of quantum physics.

Novel receivers based on quantum physics are required in order to attain these ultimate data rates, which are fundamentally superior to the rates supported by conventional optical receivers. However, a structured methodology for designing optimal versions of such quantum receivers had remained unknown. A recently proposed quantum decoding algorithm known as belief propagation with quantum messages promises to be a near-optimal design methodology.

The project will investigate the use of this algorithm to design quantum receivers for a large class of communication codes and optical modulation formats. The receiver designs are known to be in principle realizable on photonic quantum hardware. The proposed project will explore alternative implementations of the quantum logic required to realize the receiver circuitry on the commercially-available photonic quantum processor of Xanadu Quantum Technologies and determine the resource-optimal implementation.

The success of this project would enable up to 5x higher optical communication rates over NASA’s future deep-space optical lasercom systems. Moreover, a successful realization of the receiver on Xanadu’s photonic processor would amount to a demonstration of quantum advantage over classical processing using a near-term noisy quantum processor in a practical application, which is an important quest in quantum information processing today.

The proposed research will provide new content for a graduate course on quantum-enhanced classical optical communications. The project will augment the continued efforts of University of Arizona and University of Texas at Austin to provide educational and research opportunities to students from under-represented groups in the emerging field of quantum information technologies.

The proposed project is aimed at designing and implementing quantum joint detection receivers (JDRs) for quantum-enhanced optical laser communication that involve pre-detection, collective, quantum-domain processing of blocks of received optical pulses. The design part of the project will utilize a quantum decoding algorithm, belief propagation with quantum messages (BPQM), which for a binary phase shift keying-modulated lasercom system based on an exemplary 5-bit tree code was recently shown to attain the quantum limit of minimum block decoding error probability.

The BPQM algorithm will be investigated for low-density parity check codes and for different optical modulation formats. Pertaining to implementation, the BPQM-based JDR design for lasercom readily translates into a quantum circuit that is executable on a near-term, non-error-corrected, photonic, noisy intermediate-scale quantum (NISQ) processor capable of performing cat-basis quantum logic.

Several alternative approaches are available to realize the elementary gates of cat-basis logic, among which the resource-optimal approach is unknown. In order to identify the optimal approach, as part of the project, theoretical and experimental noise models will be built for the basic building blocks of the different approaches using the photonic quantum hardware of Xanadu Quantum Technologies.

The expected performance of the BPQM-based JDR for simple 3- and 5-bit tree code examples will be numerically simulated. A complete blueprint of the optical quantum circuit of the BPQM-JDR in terms of the identified optimal implementation of cat-basis logic for the 5-bit linear tree code will be developed and realized over Xanadu’s photonic quantum processor.

Universal quantum-logic manipulation of modulated quantum light underlies a number of other quantum-enhanced classical communications and sensing applications, e.g., entanglement-assisted classical radio-frequency communications and sensors such as distributed clocks and long-baseline telescopes. NISQ-era photonic quantum hardware can potentially already power some of these applications but require a concerted quantum engineering effort to leverage their existing capabilities. The proposed project will accelerate this process for strong societal and economic impact.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.