We investigate the quantum non-demolition (QND) measurement of an atomic population based on a heterodyne detection and show that the induced back-action allows to prepare both spin-squeezed and Dicke states. We use a wavevector formalism to describe the stochastic process of the measurement and the associated atomic evolution. Analytical formulas of the atomic distribution momenta are derived in the weak coupling regime both for short and long time behavior, and they are in good agreement with those obtained by a Monte-Carlo simulation. The experimental implementation of the proposed heterodyne detection scheme is discussed. The role played in the squeezing process by the spontaneous emission is considered.
Cross-correlation heterodyne detectors exhibit the potential for suppression of the detection quantum noise below shot noise without use of optical squeezing for capturing weak optical signals in low frequency bands. To understand the underlying mechanism, we develop a quantum theory to describe the noise performance of cross-correlation heterodyne detectors. By calculating the cross spectral density (CSD) of the photocurrent fluctuations from a cross-correlation heterodyne detector, we prove that its noise performance can break the shot noise limit and exceed that of a regular heterodyne dete…
We explore the phenomena of quadrature squeezing of photons in the Two-Photon Dicke Model under the mean-field approximation in the thermodynamic limit. The strength of photon squeezing is maximized in the region where the coupling strength is of the same order of magnitude as one of the fundamental frequency of the system. This particular region is termed as the unbounded region. The squeezing of the photonic quadratures can be observed only in the superradiant phase where the squeezing is well beyond the standard quantum limit both near the quantum critical point as well as the unbounded reg…
Spin-Squeezing-Enhanced Charging for Quantum Dicke Batteries
Fujian Key Laboratory of Quantum Information and Quantum Optics, Fuzhou University（福建量子信息与量子光学重点实验室，福州大学）；Department of Physics, Fuzhou University（福州大学物理系）；School of Physics and Electronic Engineering, Hubei University of Arts and Science（湖北文理学院物理与电子工程学院）；Quantum Information Physics Theory Research Team, Center for Quantum Computing, RIKEN（理化学研究所量子计算中心量子信息物理理论研究组）
Dicke materials as a resource for quantum squeezing
Rice University（莱斯大学）；Smalley-Curl Institute, Rice University（斯莫利-柯尔研究所，莱斯大学）；Department of Physics and Astronomy, Rice University（莱斯大学物理与天文学系）；Department of Materials Science and NanoEngineering, Rice University（莱斯大学材料科学与纳米工程系）；Max Planck Institute for the Structure and Dynamics of Matter（马克斯·普朗克物质结构动力学研究所）；Yokohama National University（横滨国立大学）；Interfaculty Graduate School of Innovative and Practical Studies, Yokohama National University（横滨国立大学跨学科创新与实践研究生院）；Department of Physics, College of Engineering Science, Yokohama National University（横滨国立大学工程科学部物理系）；Department of Physics, Graduate School of Engineering Science, Yokohama National University（横滨国立大学工学研究科物理系）；Institute for Multidisciplinary Sciences, Yokohama National University（横滨国立大学多学科科学研究院）
We introduce tqix.pis, a library of tqix, for quantum dynamics simulation of spin ensembles. The library emulates a dynamic process by a quantum circuit, including initializing a quantum state, executing quantum operators, and measuring the final state. It utilizes collective processes in spin ensembles to reduce the dimension from exponentially to quadratically with the number of particles, i.e., the quantum state spans in Dicke basis. It also facilitates the simulation time with multi-core processors and Graphics Processing Units. The library is thus applicable for the simulation of ensemble…
Entanglement and extreme spin squeezing of unpolarized states
我们提出的标准来检测自旋j粒子的宏观合奏使用的方差和集体自旋分量的二阶矩的纠缠的深度。检测到的状态的类别超越了传统的自旋压缩状态，包括迪克状态和其他非极化状态。推导出的标准是很容易的数值评估，即使是非常多的粒子系统和优于过去的方法，特别是在实际情况下，噪声是存在的。我们还推导出解析下界的基础上线性化我们的标准，这使得有可能定义自旋压缩参数的Dicke状态。此外，我们还从[A. S. Sorensen和K. Molmer，Phys. Rev. Lett. 86，4431（2001）]。我们还将我们的结果扩展到具有波动粒子数的系统。
The dynamics of squeezing across quantum phase transition in two basic models, viz., the one-axis twisting model in transverse field and the Dicke model, is investigated using Holstein-Primakoff representation in the large spin limit. Near the phase boundary between the disordered (normal) and the ordered (superradiant) phase, the strength of spin and photon squeezing and the duration of time for which the system stays in the highly squeezed state are found to exhibit strong power-law growth with distance from the quantum critical point. The critical exponent for squeezing time is found to be …
Optical squeezing mediated by levitated oscillators at their quantum ground state
CNR-INO（意大利国家研究委员会红外光学研究所）；Dipartimento di Fisica e Astronomia, Univ. Di Firenze（佛罗伦萨大学物理与天文系）；INFN, Sezione di Firenze（意大利国家核物理研究院佛罗伦萨分部）；European Laboratory for Non-Linear Spectroscopy (LENS)（欧洲非线性光谱学实验室）
In a view of recent proposals for the realization of anisotropic light-matter interaction in such platforms as (i) non-stationary or inductively and capacitively coupled superconducting qubits, (ii) atoms in crossed fields and (iii) semiconductor heterostructures with spin-orbital interaction, the concept of generalized Dicke model, where coupling strengths of rotating wave and counter-rotating wave terms are unequal, has attracted great interest. For this model, we study photon fluctuations in the critical region of normal-to-superradiant phase transition when both the temperatures and number…
Asymmetry effects in homodyne and heterodyne measurements: Positive operator-valued measures and asymptotic security of Gaussian-continuous-variable quantum key distribution
ITMO University（伊托夫大学）；Laboratory for Quantum Communications, ITMO University（伊托夫大学量子通信实验室）；Laboratory of Quantum Processes and Measurements, ITMO University（伊托夫大学量子过程与测量实验室）
The generated magnitude of quadrature squeezing in a cavity-coupled ensemble, which is continuously driven using a coherent off-axis field, is theoretically explored. Using a truncated set of equations-of-motion derived from a Dicke Hamiltonian, steady-state quadrature squeezing of the cavity field is numerically calculated to approach a limit of -3 dB, while frequency-modulated quadrature squeezing approaches a limit of -14 dB, in the absence of pure-dephasing, and as a function of the ensemble's size and detuning. The impact of pure-dephasing on steady-state quadrature squeezing is shown to …
In this work, we consider the estimation of single mode Gaussian states using four different measurement schemes namely: i) homodyne measurement, ii) sequential measurement, iii) Arthurs-Kelly scheme, and iv) heterodyne measurement, with a view to compare their relative performance. To that end, we work in the phase space formalism, specifically at the covariance matrix level, which provides an elegant and intuitive way to explicitly carry out involved calculations. We show that the optimal performance of the Arthurs-Kelly scheme and the sequential measurement is equal to the heterodyne measur…
Quantum spin squeezing is an important resource for quantum information processing, but its squeezing degree is not easy to preserve in an open system with decoherence. Here, we propose a scheme to implement single-photon-triggered spin squeezing with decoherence reduction in an open system. In our system, a Dicke model (DM) is introduced into the quadratic optomechanics, which can be equivalent to an effective DM manipulated by the photon number. Besides, the phonon mode of the optomechanical system is coupled to a squeezed vacuum reservoir with a phase matching, resulting in that the thermal…
Beating noise in frequency estimation with squeezing and memory in continuous-variable systems
Harish-Chandra Research Institute（哈里什-昌德拉研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Università di Milano（米兰大学）；INFN, Sezione di Milano（意大利国家核物理研究所米兰分部）
A recent experiment demonstrated heterodyne detection-based frequency measurements with superradiant pulses from coherently pumped strontium atoms in an optical lattice clock system, while another experiment has analyzed the statistics of superradiant pulses from incoherently pumped calcium atoms in a similar system. In this article, we propose to perform heterodyne detection of the superradiant pulses from the calcium atoms, and analyze theoretically the corresponding atomic ensemble dynamics in terms of the rotation of a collective spin vector and the incoherent quantum jumps among superradi…
Multiensemble Superradiance for Distributed Quantum Sensing
College of Physical Science and Technology, Central China Normal University（华中师范大学物理科学与技术学院）；School of Science, Hubei University of Technology（湖北工业大学理学院）
The ground state of the photon-matter coupled system described by the Dicke model is found to be perfectly squeezed at the quantum critical point of the superradiant phase transition (SRPT). In the presence of the counter-rotating photon-atom coupling, the ground state is analytically expressed as a two-mode squeezed vacuum in the basis of photons and atomic collective excitations. The variance of a quantum fluctuation in the two-mode basis vanishes at the SRPT critical point, with its conjugate fluctuation diverging, ideally satisfying the Heisenberg uncertainty principle.
On-chip Dicke-type magnon polaritons in the ultrastrong coupling regime via spatially separated nanomagnets
Kyoto University（京都大学）；Center for Spintronics Research Network, Institute for Chemical Research, Kyoto University（京都大学化学研究所在旋电子学研究网络中心）；Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften（巴伐利亚科学院瓦尔特-迈斯纳研究所）；Technical University of Munich, TUM School of Natural Sciences, Physics Department（慕尼黑工业大学自然科学学院物理系）；Osaka Metropolitan University（大阪公立大学）；Munich Center for Quantum Science and Technology (MCQST)（慕尼黑量子科学与技术中心）
