The efficient detection of a single spin is a significant goal of improving the sensitivity of quantum magnetic-field sensors. Recent results show that a specific type of entanglement such as Greenberger-Horne-Zeilinger (GHZ) states can be used as a resource to improve the performance of single spin detection. However, scalable generation of the GHZ states is experimentally difficult to realize. It is desirable to use a practical entangled state that can be easily generated. In this paper, we propose the efficient detection of a single spin with Dicke states. We show a way to prepare and measure Dicke states via a global control. Moreover, we investigate how dephasing due to unwanted coupling with the environment affects the performance of our proposal, and show that single spin detection with Dicke states with dephasing has a significant advantage over the classical strategy with separable states. Our results are important toward realizing entanglement enhanced single spin detection.
We consider an exactly solvable inhomogeneous Dicke model which describes an interaction between a disordered ensemble of two-level systems with single mode boson field. The existing method for evaluation of Richardson-Gaudin equations in the thermodynamical limit is extended to the case of Bethe equations in Dicke model. Using this extension, we present expressions both for the ground state and lowest excited states energies as well as leading-order finite-size corrections to these quantities for an arbitrary distribution of individual spin energies. We then evaluate these quantities for an e…
Using the exact eigenstates of the inhomogeneous Dicke model obtained by numerically solving the Bethe equations, we study the decay of bosonic excitations due to the coupling of the mode to an ensemble of two-level (spin 1/2) systems. We compare the quantum time-evolution of the bosonic mode population with the mean field description which, for a few bosons agree up to a relatively long Ehrenfest time. We demonstrate that additional excitations lead to a dramatic shortening of the period of validity of the mean field analysis. However, even in the limit where the number of bosons equal the nu…
Reinforcement Learning for Charging Optimization of Inhomogeneous Dicke Quantum Batteries
CFINS, Department of Automation, Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing, 100084, China（信息科学与技术北京国家研究中心，自动化系，清华大学，北京，100084，中国）；School of Integrated Circuits, Tsinghua University, Beijing, 100084, China（集成电路学院，清华大学，北京，100084，中国）
We study theoretically the collective E$\otimes$e Jahn-Teller-Dicke distortion in a system of trapped ions. We focus in the limit of infinite range interactions in which an ensemble of effective spins interacts with two collective vibrational modes with U(1) symmetric couplings. Our model is exactly solvable in the thermodynamical limit and it is amenable to be solved by exact numerical diagonalization for a moderate number of ions. We show that trapped ions are ideally suited to study the emergence of spontaneous symmetry breaking of a continuous symmetry and magnetic structural phase transit…
We study the constructions of Dicke states of identical particles of spin-$1$, $3/2$ and $2$ in the number representation with given particle number $N$ and magnetic quantum number $M$. The complete bases and corresponding coefficients in the Dicke states are given, in terms of which the Dicke states are explicitly expressed in the number representation. As a byproduct, a rule of how to construct all the anti-symmetric states in these high spin systems is given. Finally, by employing the negativity as the entanglement measure, we explore the entanglement properties for spin-$1$ cases including…
We present a Dicke state preparation scheme which uses global control of $N$ spin qubits: our scheme is based on the standard phase estimation algorithm, which estimates the eigenvalue of a unitary operator. The scheme prepares a Dicke state non-deterministically by collectively coupling the spins to an ancilla qubit via a $ZZ$-interaction, using $\ceil*{\log_2 N} + 1$ ancilla qubit measurements. The preparation of such Dicke states can be useful if the spins in the ensemble are used for magnetic sensing: we discuss a possible realization using an ensemble of electronic spins located at diamon…
Generalized Dicke models can be implemented in hybrid quantum systems built from ensembles of nitrogen-vacancy (NV) centers in diamond coupled to superconducting microwave cavities. By engineering cavity assisted Raman transitions between two spin states of the NV defect, a fully tunable model for collective light-matter interactions in the ultra-strong coupling limit can be obtained. Our analysis of the resulting non-equilibrium phases for a single cavity and for coupled cavity arrays shows that different superradiant phase transitions can be observed using existing experimental technologies,…
We realize a spin-1 Dicke model using magnetic sub-levels of the lowest F=1 hyperfine level of $^{87}$Rb atoms confined to a high finesse cavity. We study this system under conditions of imbalanced driving, which is predicted to have a rich phase diagram of nonequilibrium phases and phase transitions. We observe both super-radiant and oscillatory phases from the cavity output spectra as predicted by theory. Exploring the system over a wide range of parameters, we obtain the boundaries between the normal, super-radiant and the oscillatory phases, and compare with a theoretical model.
We consider the high probability state transfers and entanglements between different nodes of the spin-1/2 chains governed by the XXZ-Hamiltonian using the inhomogeneous stationary external magnetic field. Examples of three-, four-, ten- and twenty-node chains are represented. A variant of realization of the proper inhomogeneous magnetic field is discussed.
Differential magnetometry with partially flipped Dicke states
University of the Basque Country UPV/EHU（巴斯克地区大学）；Universitat de València（瓦伦西亚大学）；CSIC（西班牙国家研究委员会）；Donostia International Physics Center DIPC（多诺斯蒂亚国际物理中心）；IKERBASQUE, Basque Foundation for Science（伊卡巴斯基克，巴斯克科学基金会）；HUN-REN Wigner Research Centre for Physics（匈牙利研究与教育网络维格纳物理研究中心）
We study the interaction of an electron/hole with inhomogeneous magnetic field in the presence of a screw dislocation. We consider the internal structure of the defect, i.e., we consider the core that gives rise to a finite size to the defect. In addition, we assume that this core determines a forbidden region for the electron/hole. Then, we solve the Schrödinger equation and show that an Aharonov-Bohm-type effect arises from the influence of the topological defect and the missing magnetic flux on the eigenvalues of energy.
We study experimentally and theoretically a dense ensemble of negatively charged nitrogen-vacancy centers in diamond coupled to a high $Q$ superconducting coplanar waveguide cavity mode at low temperature. The nitrogen-vacancy centers are modeled as effective spin one defects with inhomogeneous frequency distribution. For a large enough ensemble the effective magnetic coupling of the collective spin dominates the mode losses and inhomogeneous broadening of the ensemble and the system exhibits well resolved normal mode splitting in probe transmission spectra. We use several theoretical approach…
We study the spin textures of a confined two-dimensional electron in inhomogeneous magnetic fields. These fields can either be external or effective fields due to a background magnetic texture in the plane in which the electron resides. By analytical considerations, WKB-type approximations, and by performing numerical diagonalizations we show that the in-plane spin field components of a single electron can form vortices while the total spin field can become a skyrmion. Most interestingly, we find that topological trivial magnetic fields can induce topological spin field configurations in the e…
We studied the transport properties of electrons in graphene as they are scattered by a double barrier potential in the presence of an inhomogeneous magnetic field. We computed the transmission coefficient and Goos-Hänchen like shifts for our system and noticed that transmission is not allowed for certain range of energies. In particular, we found that, in contrast to the electrostatic barriers, the magnetic barriers are able to confine Dirac fermions. We also established some correlation between the electronic transmission properties of Dirac fermions with the Goos-Hänchen like shifts, as ref…
This paper investigates the local quantum correlations (LQU), including entanglement, of two gravitational cat states subjected to an inhomogeneous magnetic field. We derived the LQU expression from the physical quantities associated with the selected system. Our findings suggest that temperature, magnetic field, and magnetic field inhomogeneity may all play a role in determining the degree of intricacy between the gravcats to some extent. Furthermore, these conclusions suggest that the thermal LQU captures a stronger quantum correlation than the entanglement. Especially true for low external …
In this work, we use the Hamiltonian of a modified Dzyaloshinskii-Moriya model and investigate the perfect transfer of the quantum state on the spin networks. In this paper, we calculate fidelity in which fidelity depends on magnetic field and another parameters. Then, by using the numerical analysis we show that the fidelity of the transferred state is determined by magnetic field $B$, exchange coupling $J$ and the Dzyaloshinskii- Moriya interaction $D$. We also found that the perfect transfer of the quantum state is possible with condition $B \gg Γ^2ω^{N/2}$ where $Γ=((J+iD)/2)$ and $ω=Γ^*/ …
Topological spin transport of photons: "magnetic monopole" gauge field in Maxwell equations and polarization splitting of rays in periodically inhomogeneous media
We propose an optimal set of quantum gates for a singlet-triplet qubit in a double quantum dot with two electrons utilizing the $S$-$T_-$ subspace. Qubit rotations are driven by the applied magnetic field and an orthogonal field gradient provided by a micromagnet. We optimize the fidelity of this qubit as a function of magnetic fields, taking advantage of "sweet spots" where the rotation frequencies are independent of the energy level detuning, providing protection against charge noise. We simulate gate operations and qubit rotations in the presence of quasistatic noise from charge and nuclear…
