[Paper Review] Deterministic multi-mode gates on a scalable photonic quantum computing platform

Mikkel V. Larsen, Xueshi Guo+3 more|arXiv (Cornell University)|Oct 27, 2020

Quantum Information and Cryptography66 references131 citations

TL;DR

This paper demonstrates the first deterministic, programmable, multi-mode quantum computation platform using continuous-variable photonic cluster states. By applying phase-programmed quadrature measurements on a large-scale 2D time-encoded cluster state, the authors implement a universal set of Gaussian gates via gate teleportation, achieving fault-tolerant quantum computing potential with telecom-wavelength compatibility and scalability.

ABSTRACT

Quantum computing can be realized with numerous different hardware platforms and computational protocols. A highly promising approach to foster scalability is to apply a photonic platform combined with a measurement-induced quantum information processing protocol where gate operations are realized through optical measurements on a multipartite entangled quantum state -- a so-called cluster state. Heretofore, a few quantum gates on non-universal or non-scalable cluster states have been, but a full set of gates for universal scalable quantum computing has not been realized. We propose and demonstrate the deterministic implementation of a multi-mode set of measurement-induced quantum gates in a large two-dimensional (2D) optical cluster state using phase-controlled continuous variable quadrature measurements. Each gate is simply programmed into the phases of the high-efficiency quadrature measurements which execute the transformations by teleportation through the cluster state. Using these programmable gates, we demonstrate a small quantum circuit consisting of 10 single-mode gates and 2 two-mode gates on a three-mode input state. On this platform, fault-tolerant universal quantum computing is possible if the cluster state entanglement is improved and a supply of Gottesman-Kitaev-Preskill qubits is available. Moreover, it operates at the telecom wavelength and is therefore network connectable without quantum transducers.

Motivation & Objective

• To develop a scalable, deterministic, and fully programmable photonic quantum computing platform based on continuous-variable measurement-based quantum computation (MBQC).
• To demonstrate universal quantum computation using only Gaussian operations and Gottesman-Kitaev-Preskill (GKP) qubits via measurement-induced gate teleportation.
• To achieve fault-tolerant quantum computation by improving cluster state entanglement and integrating GKP-encoded qubits.
• To enable network connectivity by operating at telecom wavelengths (1550 nm) without quantum transducers.
• To establish a hardware-software interface where quantum circuits are compiled into phase settings for high-efficiency homodyne measurements.

Proposed method

• The platform uses a time-encoded 1D cluster state coiled into a 2D cylindrical structure via Nτ-delay lines, with spatial modes A and B in temporal modes k.
• Squeezed light from two optical parametric oscillators (OPOs) at 1550 nm generates the cluster state via interference in an imbalanced interferometer.
• Quantum gates are implemented by projective quadrature measurements on cluster state modes using a beam-splitter and tunable homodyne detectors with controllable local oscillator phases.
• Gate operations are programmed entirely by adjusting the measurement basis (phase) of the quadrature measurements, enabling gate teleportation through the cluster state.
• The computation scheme uses chronological measurement order along the cluster state cylinder, matching information flow and eliminating need for optical memory.
• The system leverages GKP encoding to enable fault-tolerance using only Gaussian operations and error correction.

Experimental results

Research questions

• RQ1 Can a scalable, deterministic, and fully programmable photonic quantum computing platform be realized using continuous-variable cluster states?
• RQ2 Can universal quantum computation be achieved using only Gaussian operations and GKP-encoded qubits via measurement-based quantum computation?
• RQ3 How does the gate noise scale with cluster state squeezing, measurement efficiency, and phase stability in a realistic experimental setup?
• RQ4 To what extent can gate fidelity be improved by optimizing pump power, optical efficiency, and squeezing bandwidth?
• RQ5 Can this platform operate at telecom wavelengths to enable future photonic network integration?

Key findings

• The authors demonstrate a fully deterministic and programmable multi-mode quantum circuit with 10 single-mode gates and 2 two-mode gates on a three-mode input state using a 2D cluster state.
• The measured single-mode gate noise is 1.6 dB (1.4V₀), consistent with theoretical predictions based on 4.4 dB of initial momentum squeezing.
• Gate noise decreases with increasing pump power and optical efficiency, saturating due to losses and phase fluctuations in the current setup.
• Theoretical analysis shows that gate noise can be reduced further with higher efficiency (≥90%) and broader squeezing bandwidth (e.g., 100 MHz vs. 7.7 MHz).
• The platform operates at 1550 nm, enabling direct network connectivity without quantum transducers.
• The system achieves universal quantum computation potential if cluster state entanglement is improved and GKP qubits are supplied, as per fault-tolerant CV MBQC models.