We investigate spin squeezing for a one-axis twisting (OAT) model coupled to a general non-Markovian environment in a finite-temperature regime. Using the non-Markovian quantum state diffusion and master equation approach, we numerically study non-Markovian spin-squeezing generation in the OAT model. Our results show that the total spin number $N$, energy ${k}_{B}T$, and certain coefficients in the OAT model can play a crucial role in generating spin squeezing. In particular, it shows that the maximum spin squeezing can be significantly enhanced when the participating environment has a relatively long memory time.
We investigate spin squeezing for a one-axis twisting (OAT) model coupled to a general non-Markovian environment in a finite-temperature regime. Using the non-Markovian quantum state diffusion and master equation approach, we numerically study non-Markovian spin-squeezing generation in the OAT model. Our results show that the total spin number N, energy kBT, and certain coefficients in the OAT model can play a crucial role in generating spin squeezing. In particular, it shows that the maximum spin squeezing can be significantly enhanced when the participating environment has a relatively long memory time.
Spin squeezing, a compelling manifestation of multiparticle entanglement, is considered one of the most promising quantum resources. Non-Markovian characteristics play a crucial role in many critical physical processes involving strong system-environment interactions. We investigate the generation of spin squeezing in a hybrid quantum system composed of silicon-vacancy color centers (SiV) and diamond acoustic waveguides in a finite-temperature non-Markovian environment. The results indicate that memory parameters, damping rates, environmental temperature, and the total spin number play critical roles in the generation of spin squeezing. By appropriately tuning these parameters, the spin-squeezing effect of the quantum system can be significantly enhanced. This study provides theoretical foundations and optimization strategies for the application of quantum systems in complex environments, such as quantum information processing and quantum precision measurement.
In this work we study One Axis Twisting (OAT) spin squeezing for metrology in the presence of decoherence. We study Linbladian evolution in the presence of both T_1 and T_2 (longitudinal and transverse relaxation processes). We show that spin squeezing can be an effective way to improve metrological accuracy even in the presence of decoherence for OAT squeezing. We show our results are not sensitive to inhomogeneity of the squeezing strength of the many spin OAT Hamiltonian and that very general squeezed states do not have entanglement enhanced decoherence. We also extend the Kitagawa-Ueda OAT squeezing formula to finite polarization.
In the absence of decay, the conditional dynamics for an open system is often describable by a non-Hermitian Hamiltonian. This study investigates spin squeezing (SS) in a non-Hermitian one-axis twisting (OAT) model. Somewhat surprisingly, SS close to the limit of Hermitian two-axis counter twisting (TACT) Hamiltonian is achievable for some parameters, which significantly improves upon the optimal value realizable by the Hermitian OAT model. The drawback is like with all conditional schemes, it takes on average longer time to evolve into a steady state, and the probability of no decay or success decreases as the number of atoms (spins) increases. The result above for the steady-state SS in a non-Hermitian OAT Hamiltonian is thus limited to small systems. For other parameter regimes, however, desirable SS arrives dynamically before a steady state is achieved, with a greatly shortened evolution time and enhanced probability of success, while still remains significantly improved over the limit of Hermitian OAT.
Squeezed states of spin systems are an important entangled resource for quantum technologies, particularly quantum metrology and sensing. Here we consider the generation of spin squeezed states by interacting the spins with a dissipative ancillary system. We show that spin squeezing can be generated in this model by two different mechanisms: one-axis twisting (OAT) and driven collective relaxation (DCR). We can interpolate between the two mechanisms by simply adjusting the detuning between the dissipative ancillary system and the spin system. Interestingly, we find that for both mechanisms, ancillary system dissipation need not be considered an imperfection in our model, but plays a positive role in spin squeezing. To assess the feasibility of spin squeezing we consider two different implementations with superconducting circuits. We conclude that it is experimentally feasible to generate a squeezed state of hundreds of spins either by OAT or by DCR.
We apply the stochastic Schr\"odinger equation approach to study the non-Markovian dynamics of quantum systems coupled to a squeezed environment. We derive the non-Markovian quantum-state-diffusion equation using coherent-state unraveling and the associated zeroth-order master equation for general models in a microscopic quantum context. Focused on a dissipative optical cavity coupled with a squeezed vacuum, the numerical simulations demonstrate the time evolution of photon numbers in an optical cavity. We observe that the long-time limits of the non-Markovian dynamics are significantly different from those of the Markovian dynamics for various memory factors and squeezing factors. Additionally, non-Markovian dynamics exhibit a distinct pattern of behavior when parameters change. Our work provides a method to study the impact of multiple parameters on the non-Markovian dynamics and long-time limits in a joint manner. The method can be further extended to squeezed finite-temperature environments.
Open-system descriptions are typically introduced by coupling a quantum system to an external environment. Here we show that a closed interacting many-body system can itself generate a controlled non-Markovian quantum channel acting on a reduced nonlinear qubit through finite-size corrections to a nonlinear mean-field limit. We demonstrate this using the Kitagawa-Ueda one-axis twisting model, H=χJz2, a paradigmatic model of collective spin dynamics, spin squeezing, and two-component Bose-Einstein condensates. Although the large-N regime of this model has been extensively studied, the conventional fixed-χ scaling does not yield a nontrivial dynamical large-N limit. In this paper, we investigate a complementary large-N formulation obtained from the double limit N→∞ and χ→O(g/N), where g is a coupling constant. We derive the leading finite-N corrections to this limit and show that they correspond to an emergent non-Markovian dephasing process, producing a Gaussian decay of the Bloch-vector coherence with characteristic timescale tφ≥N/(2g). Exact finite-N calculations demonstrate that this effective open-system description becomes quantitatively accurate for systems containing on the order of one hundred qubits. The resulting framework provides a microscopic realization of non-Markovian dephasing generated intrinsically by a closed many-body system and enables efficient simulation of collective quantum dynamics beyond unitary mean-field theory. These results link the long-studied phenomenon of phase diffusion in atomic ensembles and Bose-Einstein condensates to the growing effort to characterize non-Markovian, beyond-Lindblad noise in quantum computing hardware, providing a rare case in which such a noise channel is derived from microscopic dynamics rather than fit phenomenologically.