The principles are elaborated which underlie the applications of general nonclassical states to communication and measurement systems. Relevant classical communication concepts are reviewed. Communication and measurement processes are compared. The possible advantages of nonclassical states in classical information transfer are assessed. The significance of novel quantum amplifiers and duplicators in communication is emphasized. A general approach is developed for determining the ultimate accuracy limit in quantum measurement systems. It is found that bandwidth or mode number is a most important parameter and ultrahigh precision measurement is possible in systems with a fixed energy but many modes. The problem of the standard quantum limit in monitoring the position of a free mass is also addressed.
su(1,1) coherent states and a normal extension of su(1,1) annihilation operator: squeezed states and the simultaneous measurement of Q^{-1}P+PQ^{-1} and Q^{-2}
We present a scheme for quantum randomness certification based on quantum steering. The protocol is one-sided device independent, providing high security, but requires only states and measurements that are simple to realise on quantum optics platforms - entangled squeezed vacuum states and homodyne detection. This ease of implementation is demonstrated by certifying randomness in existing experimental data and implies that giga-hertz random bit rates should be attainable with current technology. Furthermore, the steering-based setting represents the closest to full device independence that can…
Two-mode squeezed number states (TMSNS) are natural generalization of two-mode squeezed vacuum states. It has been known that every TMSNS is entangled whenever the squeezing parameter is non-zero. For a pair of entangled pure states Nielsen's majorization theorem tells us whether one state can be transformed into the other state through local operation and classical communication based on the majorization property on their probability distributions of Schmidt bases. In this report we find two examples of majorization relations for a set of TMSNS.
Pulsed pumped four-wave mixing process via $χ^{(3)}$ non-linearity in optical fiber can generate optical pulses with continuous variable quantum correlation. However, pair-wise correlation of the generated pulses in this system has not been studied. Here we report a time-domain measurement of an intensity difference squeezed state generated in fiber. With a fast response differential detection system, we show the generated twin-beam pulses are pair-wisely correlated, and -3.8 dB (-8.1 dB after detection losses correction) intensity difference squeezing degree is measured in time-domain. Our re…
Full-Period Optical Phase Estimation with Heisenberg Scaling Using Displaced Squeezed States and Gaussian Measurements
Institute for Quantum Science and Technology, University of Calgary（卡尔加里大学量子科学与技术研究所）；Center for Quantum Information and Control, Department of Physics and Astronomy, University of New Mexico（新墨西哥大学物理与天文系量子信息与控制中心）；Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理科学研究所）
Squeezed states of harmonic oscillators are a central resource for continuous-variable quantum sensing, computation and communication. Here we propose a method for the generation of very good approximations to highly squeezed vacuum states with low excess anti-squeezing using only a few oscillator-qubit coupling gates through a Rabi-type interaction Hamiltonian. This interaction can be implemented with several different methods, which has previously been demonstrated in superconducting circuit and trapped-ion platforms. The protocol is compatible with other protocols manipulating quantum harmo…
A comparative study of protocols for secure quantum communication under noisy environment: single-qubit-based protocols versus entangled-state-based protocols
We calculate the Holevo Cramér-Rao bound for estimation of the displacement experienced by one mode of an two-mode squeezed vacuum state with squeezing r and find that it is equal to 4exp(-2r). This equals the sum of the mean squared error obtained from a dual homodyne measurement, indicating that the bound is tight and that the dual homodyne measurement is optimal.
Adaptive phase estimation with two-mode squeezed-vacuum and parity measurement
一种基于在马赫-曾德尔干涉仪输出端测量双模压缩真空态宇称的相位估计方案表明，Cramér-Rao灵敏度为亚海森堡[Phys.\修订版本\ Lett. {\bf 104}，103602（2010）]。然而，这些测量是有问题的，因此尚不清楚是否可以通过有限数量的测量来获得这种灵敏度。该灵敏度仅针对接近零的相位，并且在该区域中存在模糊性的问题，因为测量不能区分相位的符号。在这里，我们考虑了有限数量的奇偶校验测量，并表明，自适应技术给出了一个高度准确的相位估计，无论相位。我们表明，海森堡极限是可达到的，其中平均光子数$\bar{n}=1$所需的试验次数约为100。我们证明了可以近似地达到Cramér-Rao灵敏度，并且估计在区间（$-π/2, π/2$）内是无模糊的.
We discuss how two-photon absorption (TPA) of squeezed and coherent states of light can be detected in measurements of the transmitted light fields. Such measurements typically suffer from competing loss mechanisms such as experimental imperfections and linear scattering losses inside the sample itself, which can lead to incorrect assessments of the two-photon absorption cross section. We evaluate the sensitivity with which TPA can be detected and find that TPA sensitivity of squeezed vacua or squeezed coherent states can become independent of linear losses at sufficiently large photon numbers…
As an application of the simultaneous and continuous measurement of noncommutative observables formulated in our previous paper [C. Jiang and G. Watanabe, Phys. Rev. A 102, 062216 (2020)], we propose a scheme to generate the pure ideal quadrature-squeezed state in a one-dimensional harmonic oscillator system by the feedback control based on such type of measurement of noncommutative quadrature observables. We find that, by appropriately setting the strengths of the measurement and the feedback control, the pure ideal quadrature-squeezed state with arbitrary squeezedness can be produced. This i…
