Gaussian Operations and Privacy

Gaussian local unitary equivalence of $n$-mode Gaussian states and Gaussian transformations by local operations with classical communication

We derive necessary and sufficient conditions for arbitrary multi--mode (pure or mixed) Gaussian states to be equivalent under Gaussian local unitary operations. To do so, we introduce a standard form for Gaussian states, which has the properties that (i) every state can be transformed into its standard form via Gaussian local unitaries and (ii) it is unique and (iii) it can be easily computed. Thus, two states are equivalent under Gaussian local unitaries iff their standard form coincides. We explicitly derive the standard form for two-- and three--mode Gaussian pure states. We then investiga…

Interconversion of pure Gaussian states using non-Gaussian operations

We analyze the conditions under which local operations and classical communication enable entanglement transformations within the set of bipartite pure Gaussian states. A set of necessary and sufficient conditions had been found in [Quant. Inf. Comp. 3, 211 (2003)] for the interconversion between such states that is restricted to Gaussian local operations and classical communication. Here, we exploit majorization theory in order to derive more general (sufficient) conditions for the interconversion between bipartite pure Gaussian states that goes beyond Gaussian local operations. While our tec…

Conversion of Gaussian states under incoherent Gaussian operations

The coherence resource theory needs to study the operational value and efficiency which can be broadly formulated as the question: when can one coherent state be converted into another under incoherent operations. We answer this question completely for one-mode continuous-variable systems by characterizing conversion of coherent Gaussian states under incoherent Gaussian operations in terms of their first and second moments. The no-go theorem of purification of coherent Gaussian states is also built. The structure of incoherent Gaussian operations of two-mode continuous-variable systems is disc…

连续变量分布式量子传感中的隐私保护

Privacy in continuous-variable distributed quantum sensing

该研究提出连续变量分布式量子传感协议，可在估计平均相位时保护本地相位，证明两方场景能实现完全隐私，三方及以上场景存在不可能性，还分析了位移、损耗的影响并完成基准对比。

Local Gaussian operations can enhance continuous-variable entanglement distillation

Entanglement distillation is a fundamental building block in long-distance quantum communication. Though known to be useless on their own for distilling Gaussian entangled states, local Gaussian operations may still help to improve non-Gaussian entanglement distillation schemes. Here we show that by applying local squeezing operations, both the performance and the efficiency of existing distillation protocols can be enhanced. We derive the optimal enhancement through local Gaussian unitaries, which can be obtained even in the most natural scenario when Gaussian mixed entangled states are share…

Discrimination of the binary coherent signal: Gaussian-operation limit and simple non-Gaussian near-optimal receivers

We address the limit of the Gaussian operations and classical communication in the problem of quantum state discrimination. We show that the optimal Gaussian strategy for the discrimination of the binary phase shift keyed (BPSK) coherent signal is a simple homodyne detection. We also propose practical near-optimal quantum receivers that beat the BPSK homodyne limit in all areas of the signal power. Our scheme is simple and does not require realtime electrical feedback.

Gaussian and Non-Gaussian operations on non-Gaussian state: engineering non-Gaussianity

Multiple photon subtraction applied to a displaced phase-averaged coherent state, which is a non-Gaussian classical state, produces conditional states with a non trivial (positive) Glauber-Sudarshan $P$-representation. We theoretically and experimentally demonstrate that, despite its simplicity, this class of conditional states cannot be fully characterized by direct detection of photon numbers. In particular, the non-Gaussianity of the state is a characteristics that must be assessed by phase-sensitive measurements. We also show that the non-Gaussianity of conditional states can be manipulate…

Quantum Non-Gaussianity From An Indefinite Causal Order of Gaussian Operations

Quantum Non-Gaussian states are considered as a useful resource for many tasks in quantum information processing, from quantum metrology and quantum sensing to quantum communication and quantum key distribution. Another useful tool that is growing attention is the newly constructed quantum switch. Its applications in many tasks in quantum information have been proved to be outperforming many existing schemes in quantum communication and quantum thermometry. In this contribution, we are addressing this later to be very useful to engineer highly non-Gaussian states from Gaussian operations whose…

概率非高斯操作在单模压缩真空态蒸馏中的优势

Advantage of probabilistic non-Gaussian operations in the distillation of single mode squeezed vacuum state

本文研究了使用光子减除、光子增加和光子催化三种概率非高斯操作对单模压缩真空态进行压缩蒸馏，推导了Wigner特征函数，发现PS和PC操作可有效蒸馏压缩而PA不能，并确定了最佳参数。

通过量子纠错调谐量子计算隐私

Tuning Quantum Computing Privacy through Quantum Error Correction

本文提出利用量子纠错技术调节量子差分隐私的隐私预算，通过决定是否应用QEC操作逐步降低噪声错误率，并推导新公式，数值模拟验证其可行性。