Preserving the complex visibility of coherently captured starlight is essential for quantum-assisted long-baseline interferometry, because this nonlocal coherence carries the spatial information needed to form astronomical images. Yet finite memory lifetime and imperfect retrieval inevitably produce storage failures; when a failed cell is heralded, its erased subsystem can leak which-node information to the environment and dephase the stored coherence. Strict finite-dimensional (\(U(1)\)) covariance further forbids uniform exact correction of all single-memory erasures. We address this combined physical and symmetry-imposed limit using local number-conserving quantum scrambling, parameter-independent pattern-conditioned recovery, and a fixed Gottesman--Jennewein--Croke receiver. We prove a channel-to-Fisher-information stability theorem that converts approximate logical recovery into an operational guarantee on receiver-accessible information over compact visibility regions. All-pattern finite-size simulations show that scrambling redistributes erasure risk and suppresses high-leakage events, while a separate equal-budget comparison identifies a shallow design that outperforms the tested deeper and charge-sector Haar-random benchmarks at the prespecified operating point. A separate compilation resolves every nontrivial recovery branch into abstract nearest-neighbor number-conserving gates. Although the present low-rate design does not yet improve fixed-total-memory throughput, it establishes a blueprint for converting spare memory capacity into protection of astronomical coherence, opening a path toward higher-rate, erasure-resilient quantum telescope architectures.
Preserving the complex visibility of coherently captured starlight is essential for quantum-assisted long-baseline interferometry, because this nonlocal coherence carries the spatial information needed to form astronomical images. Yet finite memory lifetime and imperfect retrieval inevitably produce storage failures; when a failed cell is heralded, its erased subsystem can leak which-node information to the environment and dephase the stored coherence. Strict finite-dimensional ((U(1))) covariance further forbids uniform exact correction of all single-memory erasures. We address this combined physical and symmetry-imposed limit using local number-conserving quantum scrambling, parameter-independent pattern-conditioned recovery, and a fixed Gottesman--Jennewein--Croke receiver. We prove a channel-to-Fisher-information stability theorem that converts approximate logical recovery into an operational guarantee on receiver-accessible information over compact visibility regions. All-pattern finite-size simulations show that scrambling redistributes erasure risk and suppresses high-leakage events, while a separate equal-budget comparison identifies a shallow design that outperforms the tested deeper and charge-sector Haar-random benchmarks at the prespecified operating point. A separate compilation resolves every nontrivial recovery branch into abstract nearest-neighbor number-conserving gates. Although the present low-rate design does not yet improve fixed-total-memory throughput, it establishes a blueprint for converting spare memory capacity into protection of astronomical coherence, opening a path toward higher-rate, erasure-resilient quantum telescope architectures.
It has been shown that shared entanglement between two telescope sites can in principle be used to localize a point source by mimicking the standard phase-scanning interferometer, but without physically bringing the light from the distant telescopes together. In this paper, we show that a receiver that employs spatial-mode sorting at each telescope site, combined with pre-shared entanglement and local quantum operations can be used to mimic the most general multimode interferometer acting on light collected from the telescopes. As an example application to a quantitative passive-imaging problem, we show that the quantum-limited precision of estimating the angular separation between two stars can be attained by an instantiation of the aforesaid entanglement based receiver. We discuss how this entanglement assisted strategy can be used to achieve the quantum-limited precision of any complex quantitative imaging task involving any number of telescopes. We provide a blueprint of this general receiver that involves quantum transduction of starlight into quantum memory banks and spatial mode sorters deployed at each telescope site, and measurements that include optical detection as well as qubit gates and measurements on the quantum memories. We discuss the relative Fisher-information contributions of local mode sorting at telescope sites vis-a-vis distributed entanglement-assisted interferometry, to the overall quantum-limited information about the scene, based on the ratio of the baseline distance to the individual telescope diameter.
Quantum techniques matter to optical astronomy when they preserve information in the parameter-bearing measurement channel after realistic loss, calibration, covariance, and inference are propagated to the final astrophysical observable. We compare 7 approaches by the quantity they change: internal optical-path delay, sub-Rayleigh source separation, coronagraphic planet throughput & stellar leakage, coherent field quadratures, nonlocal complex visibility, null depth, active phase sensing. In an Earth-analog astrometry case, 6-dB squeezed internal metrology improves the measured phase quadrature by 1.58 and the complete readout by ~1.20, but fixed-time planet-mass precision by only 1.010 (95 % interval 1.005-1.045); mission duration, useful baseline, cadence, calibration have greater modeled leverage. For a close young binary, signed spatial-mode demultiplexing preserves sub-Rayleigh orbital information that is substantially degraded in the tested direct-imaging comparator. A representative matched-model calculation gives a dynamical-mass RMSE gain 1.77 1.47-2.15). For illustrative equal-prior pre-main-sequence predictions at 0.10 and 0.12M⊙, mass precisions of 15%, 10%, 7% correspond to correct-selection probabilities of ~73%, 82%, 90%. The numerical gain remains provisional because the event-level continuous-image comparator, strict tail convergence, externally measured broadband transfer matrix, and finite-photon calibration are not yet closed. Modal coronagraphy and quantum-enhanced heterodyne reception define conditional receiver opportunities, while the nonlocal, nuller, and prepared-NOON cases identify physical bottlenecks that prevent an astrophysical advantage in the stated configurations. The common result is that quantum technology is most valuable when it changes an information-bearing observable and that channel remains consequential in the final science measurement.
Imaging astrophysical sources with a multi-station interferometer is intrinsically a multiparameter quantum-estimation problem. {Using tools from multiparameter quantum metrology,} we show that time-resolved repetitive or adaptive measurements in an N-station array suffer a fundamental array-level incompatibility among visibility estimators. Collective measurements, {which coherently process the received starlight across multiple time bins in a single joint readout}, remove the array-size penalty up to an order-unity factor, yielding an asymptotic O(N) enhancement for the {directional-averaged} SNR of visibility measurement. We then propose a memory-assisted interferometric architecture designed to implement collective readout through coherent storage and joint quantum processing. Imaging simulations and Fisher-information analyses demonstrate that collective measurements improve image reconstruction in near-term arrays and enhance the resolving power of future long-baseline architectures, with pronounced benefits for representative AGN targets such as NGC~4151 and 3C~273. These results highlight collective measurement as a promising building block for future quantum-assisted interferometric arrays for stellar imaging.
Can a larger quantum memory compensate for a less reliable one? This paper answers that question for optical heterodyne quantum conditional entropy under a total photon budget and a strict physical memory dimension. It separates an uncertainty loss that additional storage can reduce from an erasure floor that no increase in dimension can remove. Preparation and noise model. The optical system has m modes and total mean photon number at most E. Its joint preparation with a memory is optimized over all normal mixed states, including arbitrary optical coherence and infinite photon tails. The input memory has dimension at most d. Independently, the entire register survives with probability 1−p or is erased into an orthogonal readable failure state. The physical output therefore has d+1 levels; a total q-qubit register permits d≤2q−1. Every event is retained, with no postselection. For heterodyne measure d2mz/πm and natural logarithms, the exact all-preparation reduction is Ver(m,d,E,p)=minrankρ≤d,Tr(Nρ)≤E{W(ρ)−(1−p)S(ρ)}. Here W is Wehrl entropy, S is von Neumann entropy and N is total photon number. The rank constraint follows from pure attainment of the original mixed optical–memory problem. The objective describes quantum side information; it is not automatically the uncertainty achieved by a classical readout of the memory. An exact reliability ceiling. Define g(x)=(1+x)ln(1+x)−xlnx, S∗=mg(E/m), the ideal unlimited-memory value Bm(E)=m−Eln(1+m/E), and aE=1−[(1+E/m)ln(1+m/E)]−1. For any target excess satisfying 0<ε<aES∗, pcrit=mg(E/m)ε. A finite register reaches Ver≤Bm(E)+ε if and only if p<pcrit. At equality only an infinite memory attains the target. Above the ceiling the target is impossible even with unlimited memory. Finite storage and reliability pay different costs. Let Sd be the largest entropy of any rank-at-most-d optical state within the same photon budget, and Δd=S∗−Sd. For 0≤p<aE, pS∗+(aE−p)Δd≤Ver−Bm(E)≤pS∗+(1−p)Δd. The first contribution survives at unlimited dimension, whereas Δd tends to zero as storage grows. An exact finite Gibbs program computes Sd, including partially occupied photon shells. The two bounds give necessary and sufficient resource tests rather than an exact full finite-dimensional frontier. The unlimited-memory floor is obtained from an explicit scalar thermal optimization. Above its energy-use crossover the attaining thermal source uses less than the allowed energy. At 0<E≤10−4, 2≤d≤m+1 and p<1/8, an explicit vacuum–one-photon entangled preparation remains globally optimal over the full preparation class. Finite examples also reserve the failure flag inside the stated register and distinguish heralded erasure from unheralded replacement. The analysis builds on Gaussian Wehrl extremality theorems established in earlier literature and on Zixuan He's previous results on ideal-memory spectrum shaping and low-photon resource laws. Its additional contribution is the optimized finite-memory erasure contract, the exact feasibility boundary and physically budgeted attaining sources. The integrated 14-page article contains the complete proofs, two figure groups, finite certificates and references.
Quantum random-access memory (QRAM) enables coherent queries to classical data. However, the O(N) qubits required for a memory with N=2n addresses make QRAM appear vulnerable to noise. Though bucket-brigade routing provides intrinsic noise resilience to reduce the error in QRAM, improving the fidelity of QRAM queries is still an important and challenging problem. We introduce a low-overhead protection framework for bucket-brigade QRAM with two complementary components. First, we propose a one-fault-tolerant repeat-until-success logical controlled-SWAP gate using the [[4,2,2]] code under erasure noise channel. Interleaved erasure checks and local recovery correct every single erasure, so the leading logical failure probability is second order in the physical erasure error rates. Second, we exploit validity constraints of bucket-brigade routing to define local parity checks directly on the router states, without adding extra data qubits to create code redundancy. Under bit-flip noise, minimum-weight perfect matching with noiseless syndrome measurements corrects single interior faults, while open spatial boundaries retain a first-order contribution in the residual bit-flip rate. Monte Carlo simulations confirm quadratic suppression for the protected controlled-SWAP and improved depth scaling for decoded QRAM router-state snapshots. The two codes admit a concatenated realization in which the inner code supplies erasure protection and the outer code optionally corrects interior logical bit flips. Together, these results show how routing constraints and a protected non-Clifford routing gate can improve QRAM reliability under biased and erasure-dominant noise.
The development of high-resolution, large-baseline optical interferometers would revolutionize astronomical imaging. However, classical techniques are hindered by physical limitations including loss, noise, and the fact that the received light is generally quantum in nature. We show how to overcome these issues using quantum communication techniques. We present a general framework for using quantum error correction codes for protecting and imaging starlight received at distant telescope sites. In our scheme, the quantum state of light is coherently captured into a nonradiative atomic state via stimulated Raman adiabatic passage, which is then imprinted into a quantum error correction code. The code protects the signal during subsequent potentially noisy operations necessary to extract the image parameters. We show that even a small quantum error correction code can offer significant protection against noise. For large codes, we find noise thresholds below which the information can be preserved. Our scheme represents an application for near-term quantum devices that can increase imaging resolution beyond what is feasible using classical techniques.