Quantum-enabled optical large-baseline interferometry: applications, protocols and feasibility

TL;DR

This work surveys the potential of quantum-enabled optical VLBI to achieve diffraction-limited imaging at optical wavelengths by leveraging pre-distributed entanglement, quantum memories, and nonlocal measurements to overcome photon loss and long baselines. It develops a two-mode continuous-variable model and uses quantum Fisher information to compare parameter estimation at optical wavelengths, tying stellar-phase information to baseline and wavelength through $\phi$ and $\gamma$. The paper maps the technological requirements (phase stabilization, time-bin multiplexing, high-cooperativity cavities, and scalable quantum memories) to a multi-layer architecture, reviews experimental progress across memory platforms and entanglement distribution, and outlines open questions and practical constraints. Its findings suggest that near-term advances in quantum control and photonic integration could enable high-fidelity, large-baseline optical VLBI, with transformative implications for astronomical imaging and Earth-geodesy.

Abstract

Optical Very Long Baseline Interferometry (VLBI) offers the potential for unprecedented angular resolution in both astronomical imaging and precision measurements. Classical approaches, however, face significant limitations due to photon loss, background noise, and the requirements for dynamical delay lines over large distances. This document surveys recent developments in quantum-enabled VLBI, which aim to address these challenges using entanglement-assisted protocols, quantum memory storage, and nonlocal measurement techniques. While its application to astronomy is well known, we also examine how these techniques may be extended to geodesy -- specifically, the monitoring of Earth's rotation. Particular attention is given to quantum-enhanced telescope architectures, including repeater-based long baseline interferometry and quantum error-corrected encoding schemes, which offer a pathway toward high-fidelity optical VLBI. To aid the discussion, we also compare specifications for key enabling technologies to current state-of-the-art experimental components, including switching rates, gate times, entanglement distribution rates, and memory lifetimes. By integrating quantum technologies, future interferometric networks may achieve diffraction-limited imaging at optical and near-infrared wavelengths, surpassing the constraints of classical techniques and enabling new precision tests of astrophysical and fundamental physics phenomena.

Figures (9)

• Figure 1: The Lense-Thirring effect: a star's orbit precesses due to the frame-dragging caused by a rotating massive object, such as a spinning black hole.
• Figure 2: Geometry for using VLBI for geodesy. The position of the reference star is assumed to be fixed, and the goal is to measure the baseline vector $\bm{B}$.
• Figure 3: Increase in the length of day since 1962 malkin2024should.
• Figure 4: The coherence time of the received signal depends inversely on the bandwidth. Signals with a path length difference larger than the coherence time will not interfere with one another. In this illustration, there is one photon shared non-locally between the two stations in bin $t_1$, and in $t_5$: the photon in $t_1$ will not interfere with the one in $t_5$.
• Figure 5: Schematic of a quantum node architecture with memory and communication qubits overcoupled to the communication bus -- a fibre -- enhanced by an optical cavity.