[Paper Review] Quantum illumination with asymmetrically squeezed two-mode light

Yonggi Jo, Taek Jeong+5 more|arXiv (Cornell University)|Mar 31, 2021

Quantum Information and Cryptography4 citations

TL;DR

This paper proposes a Gaussian quantum illumination protocol using asymmetrically squeezed two-mode (ASTM) light, generated by applying independent single-mode squeezing to each mode of an initial two-mode squeezed vacuum (TMSV) state. The method enhances target detection performance—especially with realistic receivers—by boosting signal-mode energy without requiring highly bright TMSV states, achieving quantum advantage over classical illumination even under practical constraints.

ABSTRACT

We propose Gaussian quantum illumination(QI) protocol exploiting asymmetrically squeezed two-mode(ASTM) state that is generated by applying single-mode squeezing operations on each mode of an initial two-mode squeezed vacuum(TMSV) state, in order to overcome the limited brightness of a TMSV state. We show that the performance of the optimal receiver is enhanced by local squeezing operation on a signal mode whereas the performance of a realistic receiver can be enhanced by local squeezing operations on both input modes. Under a fixed mean photon number of the signal mode, the ASTM state can be close to the TMSV state in the performance of QI while there is a threshold of beating classical illumination in the mean photon number of the initial TMSV state. We also verify that quantum discord cannot be a resource of quantum advantage in the Gaussian QI using the ASTM state, which is a counterexample of a previous claim.

Motivation & Objective

• Address the challenge of generating bright two-mode squeezed vacuum (TMSV) states for quantum illumination, which is technologically difficult with current capabilities.
• Overcome the limited brightness of TMSV states by applying local squeezing operations on signal and idler modes to increase signal energy while preserving quantum correlations.
• Demonstrate that local squeezing on both modes enhances performance in realistic receivers, even when optimal receivers only benefit from signal-mode squeezing.
• Challenge the claim that quantum discord is the primary resource for quantum advantage in Gaussian quantum illumination by providing a counterexample.

Proposed method

• Generate an ASTM state by applying independent single-mode squeezing operations to each mode of an initial TMSV state, increasing the mean photon number on both signal and idler modes.
• Use the quantum Chernoff bound (QCB) to evaluate the optimal receiver's performance, assuming unitary operations can be applied before measurement.
• Implement a realistic receiver based on the displaced-homodyne two-mode (dHTD) detection scheme to assess practical performance under realistic constraints.
• Compare the error rates of target detection between the ASTM-based QI, conventional QI using bright TMSV states, and classical illumination (CI) using coherent states with homodyne detection.
• Analyze quantum discord in the ASTM state to assess its role in enabling quantum advantage, using the quantum discord as a potential resource metric.
• Systematically vary local squeezing parameters (N₁, N₂) and relative squeezing angles (φ₁ − φ₂) to determine optimal configurations for detection performance.

Experimental results

Research questions

• RQ1 Can local squeezing operations on both signal and idler modes improve the performance of quantum illumination in realistic receivers, even when the optimal receiver only benefits from signal-mode squeezing?
• RQ2 Is there a threshold in the initial TMSV state's mean photon number below which the ASTM-based QI cannot outperform classical illumination?
• RQ3 Does quantum discord serve as a sufficient resource for quantum advantage in Gaussian quantum illumination, as previously claimed?
• RQ4 How does the relative phase between local squeezing operations affect the detection performance in the dHTD receiver?
• RQ5 Can the ASTM state achieve quantum advantage over classical illumination under fixed signal-mode mean photon number, despite not matching the performance of a bright TMSV state?

Key findings

• Local squeezing on the signal mode enhances the performance of the optimal receiver, while local squeezing on the idler mode has no effect under the quantum Chernoff bound analysis.
• In realistic dHTD receivers, local squeezing on both signal and idler modes improves detection performance, with the best performance achieved when both squeezing parameters are equal (N₁ = N₂).
• The ASTM state can achieve quantum advantage over classical illumination under the same signal energy, even when the initial TMSV state has a low mean photon number (e.g., N₀ = 1), provided the squeezing parameters are sufficiently high.
• There exists a threshold in the initial TMSV state’s mean photon number below which the ASTM-based QI cannot outperform classical illumination, indicating a practical limit for the protocol’s effectiveness.
• The protocol provides a counterexample to the claim that quantum discord is the resource for quantum advantage in Gaussian QI, as quantum discord does not correlate with performance gains in this setup.
• ROC curves show that the ASTM-based QI outperforms classical illumination under the same signal energy, with the best performance occurring at φ₁ = φ₂, confirming the importance of phase alignment in local squeezing operations.