XuBo Zou, K. Pahlke, W. Mathis
We present a scheme to generate arbitrary superposition of the Dicke states of excitons in optically driven quantum dots. This proposal is based on a sequence of laser pulses, which are tuned appropriately to control transitions on Dicke state. It is shown that N laser pulses are needed to generate arbitrary superposition of the Dicke states of N quantum dots.
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Pairwise correlation is really an important property for multi-qubit states. For the two-qubit X states extracted from Dicke states and their superposition states, we obtain a compact expression of the quantum discord by numerical check. We then apply the expression to discuss the quantum correlation of the reduced two-qubit states of Dicke states and their superpositions, and the results are compared with those obtained by entanglement of formation, which is a quantum entanglement measure.
Dicke superposition probes for noise-resilient Heisenberg and super-Heisenberg Metrology
本文研究了在噪声环境下使用迪克态超位置探针进行量子相位传感，探讨了一种在单体和双体相互作用哈密顿量下生成参数编码的迪克态超位置状态，展示了其在相位阻尼噪声下的增强鲁棒性及良好的计量性能。
On-chip generation and collectively coherent control of the superposition of the whole family of Dicke states
该研究利用硅光子芯片从两个微谐振器产生四光子，并通过片上线性光学电路实现任意激发数四光子 Dicke 态全族叠加态的集体相干控制。
Nuclear excitons known from Mössbauer spectroscopy describe coherent excitations of a large number of nuclei -- analogous to Dicke states (or Dicke super-radiance) in quantum optics. In this paper, we study the possibility of constructing a laser based on these coherent excitations. In contrast to the free electron laser (in its usual design), such a device would be based on stimulated emission and thus might offer certain advantages, e.g., regarding energy-momentum accuracy. Unfortunately, inserting realistic parameters, the window of operability is probably not open (yet) to present-day tech…
We obtain exact dynamics of a two-qubit central spin model (CSM) consisting of two interacting qubits homogeneously coupled to a spin bath via the $XXZ$-type coupling, with the bath initially prepared in linear superpositions of the symmetric Dicke states. Using the interaction picture Hamiltonian with respect to the non-spin-flipping part of the model, we derive a sequence of equations of motion within each magnetization sector satisfied by the probability amplitudes of the time-evolved state. These equations of motion admit analytical solutions for the single-qubit CSM in which one of the tw…
We investigate prospects of using counter-rotating vortex superposition states in non-equilibrium exciton-polariton Bose-Einstein condensates for the purposes of Sagnac interferometry. We first investigate the stability of vortex-antivortex superposition states, and show that they survive at steady-state in a variety of configurations. Counter-rotating vortex superpositions are of potential interest to gyroscope and seismometer applications for detecting rotations. Methods of improving the sensitivity are investigated by targeting high momentum states via metastable condensation, and the appli…
We propose a method to create selective interactions with Dicke-Stark model by means of time-dependent perturbation theory. By choosing the proper rotating framework, we find that the time oscillating terms depend on the number of atomic excitations and the number of photonic excitations. Consequently, the Rabi oscillation between selective states can be realized by properly choosing the frequency of the two-level system. The second order selective interactions can also be studied with this method. Then various states such as Dicke states, superposition of Dicke states and GHZ states can be cr…
Simple ways of preparing qudit Dicke states
本文提出通过确定性和概率性方法在量子比特计算机上制备量子比特狄克态，方法简洁且高效。
For the excitons in the quantum well placed within a leaky cavity, the quantum decoherence of a mesoscopically superposed states is investigated based on the factorization theory for quantum dissipation. It is found that the coherence of the exciton superposition states will decrease in an oscillating form when the cavity field interacting with the exciton is of the form of quasimode. The effect of the thermal cavity fields on the quantum decoherence of the superposition states of the exciton is studied and it is observed that the higher the temperature of the environment is, the shorter the d…
We propose a robust scheme for generating macroscopic superposition states of spin or motion with the aid of a single photon. Shaping the wave packet of the photon enables high-fidelity preparation of non-classical states of matter even in the presence of photon loss. Success is heralded by photodetection, enabling the scheme to be implemented with a weak coherent field. We analyze applications to preparing Schrödinger cat states of a collective atomic spin or of a mechanical oscillator coupled to an optical resonator. The method generalizes to preparing arbitrary superpositions of coherent st…
We propose an experimentally accessible procedure for conditional preparation of highly non-classical states of collective spin of an atomic ensemble. The quantum state engineering is based on a combination of QND interaction between atoms and light previously prepared in a non-Gaussian state using photon subtraction from squeezed vacuum beam, homodyne detection on the output light beam, and a coherent displacement of atomic state. The procedure is capable of non-deterministic preparation of a wide class of superpositions of atomic Dicke states. We present several techniques to optimize the pe…
Constant-depth adaptive preparation of Dicke and symmetric states
本研究提出精确常深度自适应协议，可制备任意Dicke态及对称态，通过均匀子集叠加态等基础模块实现，辅助量子比特开销为多项式级，并行重复可指数抑制失败概率。
We study trajectories of collective spin states of an ensemble of spinors. The spinors considered here are either trapped ions in free space or atoms confined in a cavity, both systems of which are engineered through their interactions with light fields to obey an effective Dicke model. In an appropriate limit of the Dicke model, one obtains one-axis twisting dynamics of the collective spin and evolution after a finite time to a spin cat state, or, in the long-time limit, the Dicke state $|S,0\rangle_x$, conditioned upon there being no photon emissions from the system (i.e., no quantum jumps).…
We propose a fast and efficient technique to create classes of highly entangled states of trapped ions, such as arbitrary Dicke states and superpositions of them, e.g. NOON states. The ions are initialized in the phonon ground state and are addressed globally with a composite pulse that is resonant with the first motional sideband. The technique operates on comparatively short time scales, as resonant interactions allow one to use the minimum laser pulse area. The number of single pulses from the composite sequence is equal to the number of ions, thus the implementation complexity grows only l…
Dicke State Generation and Extreme Spin Squeezing via Rapid Adiabatic Passage
本文提出在Dicke态基上利用快速绝热通道生成具有最大量子Fisher信息的纠缠态，突破相位灵敏度经典极限，且方案对驱动场变化鲁棒、时间标度优越。
Collective charging of an organic quantum battery
本文研究由一维分子聚集体与单模腔耦合构成的有机量子电池的集体充电，发现存在最优激子-激子相互作用使存储能量密度和充电功率密度最大化，并在特定归一化条件下展现出超越Dicke QB的量子优势。
Extending the self-discharge time of Dicke quantum batteries using molecular triplets
本文提出利用分子三重态延长Dicke量子电池储能寿命，通过多层微腔中吸收层向存储层三重态的能量转移，识别并实验验证了三重态-极化激元共振机制，为抑制超辐射损耗和优化器件性能提供了新途径。
Symmetric ensembles of neutral atoms interacting via the Rydberg blockade are well-described by the Jaynes-Cummings Hamiltonian. We use this framework to study the problem of generating arbitrary superpositions of Dicke states of hyperfine qubits in such ensembles. The combination of the symmetric Rydberg blockade and microwaves that drive the qubits with a time-dependent phase is sufficient to make these ensembles completely controllable, in the sense that one can generate an arbitrary unitary transformation on the system. We apply this to the problem of state mapping. With currently feasible…
We consider the Dicke Hamiltonian, a simple quantum-optical model which exhibits a zero-temperature quantum phase transition. We present numerical results demonstrating that at this transition the system changes from being quasi-integrable to quantum chaotic. By deriving an exact solution in the thermodynamic limit we relate this phenomenon to a localisation-delocalisation transition in which a macroscopic superposition is generated. We also describe the classical analogues of this behaviour.
Multiclass Portfolio Optimization via Variational Quantum Eigensolver with Dicke State Ansatz
本文提出一种基于变分量子特征求解器和Dicke态的多类投资组合优化框架，通过引入多个参数化Dicke态来显式纳入分散化约束，提升收敛速度和求解精度。
Collective emission behavior is usually described by the decay dynamics of the completely symmetric Dicke states. To study a more realistic scenario, we investigate alternative initial states inducing a more complex time evolution. Superposition states of the fully inverted Dicke state and the Dicke ground state with unequal mutual weights are studied as examples as well as superradiance stemming from atoms in clusters separated by more than one wavelength. The Monte Carlo wave function method serves as framework to study the dynamics of quantum states, which is determined by quantum jumps on …
The Dicke state $|D_k^n\rangle$ is an equal-weight superposition of all $n$-qubit states with Hamming Weight $k$ (i.e. all strings of length $n$ with exactly $k$ ones over a binary alphabet). Dicke states are an important class of entangled quantum states that among other things serve as starting states for combinatorial optimization quantum algorithms. We present a deterministic quantum algorithm for the preparation of Dicke states. Implemented as a quantum circuit, our scheme uses $O(kn)$ gates, has depth $O(n)$ and needs no ancilla qubits. The inductive nature of our approach allows for lin…
We present an effective method of coherent state superposition (cat state) generation using single trapped ion in a Paul trap. The method is experimentally feasible for coherent states with amplitude $α\le 2$ using available technology. It works both in and beyond the Lamb-Dicke regime.
When a semiconductor absorbs light, the resulting electron-hole superposition amounts to a uncontrolled quantum ripple that eventually degenerates into diffusion. If the conformation of these excitonic superpositions could be engineered, though, they would constitute a new means of transporting information and energy. We show that properly designed laser pulses can be used to create such excitonic wave packets. They can be formed with a prescribed speed, direction and spectral make-up that allows them to be selectively passed, rejected or even dissociated using superlattices. Their coherence a…
We propose a theoretical scheme to show the possibility of generating motional nonlinear coherent states and their superposition for an undamped vibrating micromechanical membrane inside an optical cavity. The scheme is based on an intensity-dependent coupling of the membrane to the radiation pressure field. We show that if the cavity field is initially prepared in a Fock state, the motional state of the membrane may evolve from vacuum state to a special type of nonlinear coherent states. By examining the nonclassical properties of the generated state of the membrane, including the quadrature …
Depth-Efficient Quantum Circuit Synthesis for Deterministic Dicke State Preparation
该研究针对确定性Dicke态制备问题，在全连通和网格两种量子比特连通约束下提出深度更优的量子电路，同时证明对应深度下界，验证构造接近最优。
The role of polaron dressing in superradiant emission dynamics
本研究聚焦激子凝聚态纳米结构中强发射体-声子耦合形成的极化子对超辐射发射的影响，通过双量子发射体模型分析极化子修饰混合亮暗狄克态的机制，发现激发激光脉长可调控超辐射衰减特性，并推导了匹配数值结果的解析表达式。
Robustness of spin state superpositions for noisy quantum metrology
该研究针对空间关联退相下的量子计量问题，通过微扰理论推导QFI的短时弱噪声公式，分析多种自旋态叠加的QFI动力学，推导特定测量灵敏度界，为噪声量子计量的鲁棒性提供理论支撑。
Space-time dual quantum Zeno effect: Interferometric engineering of open quantum system dynamics
本文从系统-环境相互作用视角研究轨迹叠加对开放量子系统的影响，发现多轨迹叠加可导致量子态冻结，呈现量子Zeno效应的时空对偶，并无需多原子相关性即可触发Dicke-like超（亚）辐射。
We demonstrate control over the spin state of a semiconductor quantum dot exciton using a polarized picosecond laser pulse slightly detuned from a biexciton resonance. The control pulse follows an earlier pulse, which generates an exciton and initializes its spin state as a coherent superposition of its two non-degenerate eigenstates. The control pulse preferentially couples one component of the exciton state to the biexciton state, thereby rotating the exciton's spin direction. We detect the rotation by measuring the polarization of the exciton spectral line as a function of the time-differen…
Polylogarithmic-Weight Dicke States in QAC$^0$ and Arbitrary Symmetric States in QAC$^0_f$
本文提出用常深电路生成超常权重迪克态，无需FANOUT门，且证明任意对称态可由FANOUT_k门在常深内生成。
In this work we demonstrate theoretically how to use external laser field to control the population inversion of a single quantum dot exciton qubit in a nanocavity. We consider the Jaynes-Cummings model to describe the system, and the incoherent losses were take into account by using Lindblad operators. We have demonstrated how to prepare the initial state in a superposition of the exciton in the ground state and the cavity in a coherent state. The effects of exciton-cavity detuning, the laser-cavity detunings, the pulse area and losses over the qubit dynamics are analyzed. We also show how to…
Short-Depth Circuits for Dicke State Preparation
本文提出短深度电路，在全连接和网格连接上高效制备任意Dicke态，深度分别为O(k log(n/k))和O(sqrt(nk))，门数为O(kn)，无需辅助比特，并推广至对称态的制备与压缩。
We explore the possibility to entangle an excitonic two-level system in a semiconductor quantum dot (QD) with a cavity defined on a photonic crystal by sweeping the cavity frequency across its resonance with the exciton transition. The dynamic cavity detuning is established by a radio frequency surface acoustic wave (SAW). It induces Landau-Zener (LZ) transitions between the excitonic and the photonic degrees of freedom and thereby creates a superposition state. We optimize this scheme by using tailored Fourier-synthesized SAW pulses with up to five harmonics. The theoretical study is performe…
We investigate the generation of multipartite entangled state in a system of N quantum dots embedded in a microcavity and examine the emergence of genuine multipartite entanglement by three different characterizations of entanglement. At certain times of dynamical evolution one can generate multipartite entangled coherent exciton states or multiqubit $W$ states by initially preparing the cavity field in a superposition of coherent states or the Fock state with one photon, respectively. Finally we study environmental effects on multipartite entanglement generation and find that the decay rate f…
A simple technique for robust generation of vibrational Fock states in a chain of trapped ions is proposed. The method is fast and easy to implement, since only a single chirped laser pulse, simultaneously addressing all of the ions, is required. Furthermore, because the approach uses collective adiabatic passage, significant fluctuations in the intensity or frequency of the laser pulse can be tolerated, and the technique performs well even on the border of the Lamb-Dicke regime. We also demonstrate how this technique may be extended in order to create non-classical superposition states of the…
Robust Excitonic Coherence Driven by In-Plane Anisotropy in a van der Waals Semiconductor
本文直接测量了二维层状ReS2中各向异性激子的相干时间T_2和布居衰减时间T_1，发现其相干性对层厚、光密度和温度具有卓越鲁棒性，并支持ReS2具有直接带隙结构。
Heralded ultrafast generation of macroscopic quantum states in matter with bright squeezed vacuum light
本文提出通过明亮压缩真空光与单次正交测量相结合，在弱耦合条件下利用正交预示制备物质的宏观量子叠加态，并展示了从Dicke态到猫态的生成过程。
Global Variational Quantum Circuits for Arbitrary Symmetric State Preparation
本文提出一种由全局单轴扭转和全局旋转组成的变分电路，无需局部寻址或辅助比特即可高效制备任意对称态，在2N/3步内实现，并演示了制备大尺寸Dicke态及量子纠错码字的高保真度方案。
Qubit Analog with Polariton Superfluid in an Annular Trap
该研究通过环形势阱中激子-极化激元超流体实现量子比特模拟，观察到反向环流涡旋态的相干振荡，调谐耦合与基态能量并通过双态模型再现动力学，为极化激元量子比特控制及量子计算应用提供基础。
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