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arXiv:2607.25702

Benchmarking Optical Receivers for Quantum Communication and Randomness Certification

Hamid Tebyanian

quant-phSubmitted Jul 28, 2026• Announced Jul 29, 2026• 0 citations
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Abstract

The choice of optical receiver determines which properties of the transmitted states remain visible in the observed data and therefore affects the performance of different quantum protocols. We compare continuous-variable, photon-counting and hybrid receivers within the same prepare-and-measure framework, using semi-device-independent randomness generation as the main case study. The measurement device is left uncharacterised, while the source is described by the Gram matrix of its pure signal states using an energy-derived overlap constraint, a magnitude-Gram benchmark or the full complex Gram matrix of a certified coherent phase-shift-keyed constellation. Within this framework, the observed receiver statistics are used to bound $H_{\min}(B|X,Λ)$ against classical side information correlated with the measurement device but independent of the input. For a fixed Gram matrix, this bound is obtained from an exact semidefinite program, with complex multi-input cases treated in block-real form and checked through the corresponding dual certificate. Photon counting alone is phase blind for fixed-modulus phase encoding and therefore certifies no worst-case randomness. Continuous-variable receivers give the highest certified entropy at moderate energy, while under the nominal source calibration a hybrid receiver performs better at low energy when the beacon-region label is retained in the output. The same receiver statistics also provide receiver-level comparisons for discrete-modulated continuous-variable quantum key distribution, quantum reading, covert communication and quantum-signature verification, without replacing the full security analysis required for each protocol.

Comments
16 pages, 14 figures

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Randomness is fundamental for secure communication and information processing. While continuous-variable optical systems offer an attractive platform for this task, certifying genuine quantum randomness in such setups remains challenging. We present a semi-device-independent scheme for randomness certification tailored to continuous-variable implementations, where the dimension assumption is operationally implemented by restricting state preparations to the two-level Fock subspace. Using standard homodyne and displacement-based measurements, we show that simple optical setups can achieve dimension-witness violations that certify positive min-entropy, even in the presence of realistic losses and misaligned reference frames. These results demonstrate that practical and scalable quantum randomness generation is achievable with minimal experimental complexity on continuous-variable platforms.
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Quantum mechanics forbids perfect discrimination of non-orthogonal states, a limitation that can be exploited to certify intrinsic randomness. Building on this principle, this thesis investigates how limits on state discrimination can be used to generate certified randomness in prepare-and-measure protocols. In particular, we study how the performance of minimum-error quantum state discrimination constrains an adversary’s ability to predict measurement outcomes, under the sole assumption of an average energy constraint on the prepared states. We show how observed discrimination performance bounds an adversary’s optimal guessing probability and yields certified min-entropy. Exact results are obtained for fixed-dimension qubit ensembles, including closed-form expressions for two-qubit preparations and extensions to general qubit ensembles. We then introduce dimension-unbounded semidefinite programming relaxations based on Gram-matrix techniques, providing device-independent bounds that rely only on the energy constraint. A central result is the identification of critical discrimination thresholds beyond which deterministic strategies are excluded and genuine quantum randomness is certified. These results establish quantum state discrimination as an operational witness for randomness generation under natural physical assumptions.
Continuous-variable source-independent quantum random number generators offer the highest generation rates among semi-device-independent protocols. In reality, the protocol design is limited due to permissible measurement configurations. In this work, we propose a rigorous security proof framework that accommodates general, infinite-dimensional positive-operator-valued measures. Building upon the numerical security proof framework, we evaluate the randomness lower bound by maximizing the eavesdropper's guessing probability. Specifically, we transform the inherently infinite-dimensional semidefinite program in Fock space into a tractable finite-dimensional one, rigorously proving that latter provides a strict upper bound to the guessing probability of the original infinite-dimensional problem. Our framework showcases its capability by certifying secure randomness using unbalanced homodyne detection with only a single quadrature measurement, thereby bypassing the traditional requirement of measuring two conjugate quadratures such as XXX and PPP. We experimentally validate our protocol on an optical platform using vacuum and weak coherent states, achieving a maximum secure randomness extraction of 1.11 bits per sample and an ultra-high generation rate of 1.776 Gbps. This work provides a flexible design for practical, high-speed quantum random number generators.