Quantized Cavity Field Research Articles

Nonclassicality in a dispersive atom–cavity field interaction in the presence of an external driving field

We investigate nonclassical properties of a state generated by the interaction of a three-level atom with a quantized cavity field and an external classical driving field. In this study, the fields being degenerate in frequency are highly detuned from the atom. The atom interacts with the quantized field in a dispersive manner. The experimental setup involves a three-level atom passing through a cavity and interacting dispersively with the cavity field mode. Simultaneously, the atom interacts with an external classical field that is in resonance with the cavity field. The three-level atom can enter the cavity in one of the bare states [Formula: see text], [Formula: see text] or [Formula: see text] or in a superposition of two of these states. In this paper, we consider superposition of [Formula: see text] and [Formula: see text]. In our analysis, we focus on the statistical properties of the cavity field after interacting with the atom. The state vector [Formula: see text] describes the entire atom–field system but we analyze the properties of the cavity field independently neglecting the atomic component of the system. For this the atom part is traced out from [Formula: see text] to acquire the cavity field state only, denoted by [Formula: see text]. We evaluate different nonclassical measures including photon number distribution, Mandel’s [Formula: see text] parameter, squeezing properties [Formula: see text] and [Formula: see text], Wigner distribution, [Formula: see text] function, second-order correlation function [Formula: see text], etc. for the obtained cavity field state.

Error-insensitive preparation of entangled states between a Josephson qubit and microwave photons via invariant-based shortcuts

Optimal preparation of quantum entanglement is of significance to information processing and state engineering. In this paper, an efficient scheme is proposed to implement error-insensitive generation of entangled states between a Josephson qubit and microwave photons by the technique of invariant-based shortcuts to adiabaticity. A superconducting qubit is dispersively coupled to a quantized cavity field of one-dimensional transmission line resonator. Within a considered subspace spanned by three composite states, we deal with an effective interaction of the composite system with two classical drivings. A maximally entangled qubit-photon state can be deterministically induced using a splitting-like quantum state transfer. To nullify the deviation errors of Rabi coupling and frequency detuning, we optimize the driving parameters and then make the entanglement creation insusceptible to these control imperfections. Thanks to the mitigation of deviation effects, robustness against the residual noisy environment could be obtained numerically. The proposed strategy could provide a promising avenue towards fast and robust information processing with superconducting circuit quantum electrodynamics.

Depiction of an external classical field effects on a four-level W-configuration atom embedded in a coherent cavity field

This paper examines the dynamics of a W-configuration four-level atom in a quantized cavity field and the system driven by an external classical field. By applying some canonical transformations, we derive analytical solutions to the Schrödinger equation for the corresponding Hamiltonian. We have analyzed the impact of the external field and detuning parameters on the system’s relative entropy of coherence, Wigner function, and Pancharatnam phase. Our findings suggest that the external field parameter greatly affects the coherence of the system, whereas the detuning parameters may increase its maximum bounds. Furthermore, we have utilized the Wigner function as a tool to measure the quantumness and classicality of the system in its phase space. Our results indicate that the external field has a greater impact on the classicality of the system than the detuning parameters. Additionally, we have observed rapid oscillations in the dynamics of the Pancharatnam phase for large detuning values. It is worth noting that the external field reduces the number of phase jumps in the system.

Quantum battery based on dipole-dipole interaction and external driving field.

The Dicke model is a fundamental model in quantum optics, which describes the interaction between quantum cavity field and a large ensemble of two-level atoms. In this work, we propose an efficient charging quantum battery achieved by considering an extension Dicke model with dipole-dipole interaction and an external driving field. We focus on the influence of the atomic interaction and the driving field on the performance of the quantum battery during the charging process and find that the maximum stored energy exhibits a critical phenomenon. The maximum stored energy and maximum charging power are investigated by varying the number of atoms. When the coupling between atoms and cavity is not very strong, compared to the Dicke quantum battery, such quantum battery can achieve more stable and faster charging. In addition, the maximum charging power approximately satisfies a superlinear scaling relation P_{max}∝βN^{α}, where the quantum advantage α=1.6 can be reached via optimizing the parameters.

Dissipation-driven formation of entangled dark states in strongly coupled inhomogeneous many-qubit systems in solid-state nanocavities

We study quantum dynamics of many-qubit systems strongly coupled to a quantized electromagnetic cavity field in the presence of decoherence and dissipation for both quantum emitters and cavity photons, taking into account the varying coupling strength of different qubits to the cavity field and the spread of their transition frequencies. Compact analytic solutions for time-dependent quantum state amplitudes and observables are derived for a broad class of open quantum systems in Lindblad approximation with the use of the stochastic Schr\"odinger equation approach. We show that depending on the initial quantum state preparation, an ensemble of qubits can evolve into a rich variety of many-qubit entangled states with destructive or constructive interference between the qubits. In particular, when only a small fraction of qubits are initially excited, the dissipation in a cavity will inevitably drive the system into robust dark states that are completely decoupled from the cavity and live much longer than the decay time of the cavity field. We also determine the conditions under which coherent coupling to the quantized cavity field overcomes the dephasing caused by a spread of transition frequencies in multiqubit systems and leads to the formation of a decoupled dark state.

ENGINEERING GEOMETRIC PHASE AND CORRELATION DYNAMICS OF NITROGEN VACANCIES IN DIAMOND INTERACTING WITH TWO NANOCAVITIES

In this paper, we study the interaction of Nitrogen Vacancies in Diamond (NVD) with quantized cavity field. The system is explored analytically and the effect of the system parameters is analyzed. The stability of a quantum system with influencing factors is investigated using the Mandal Parameter. The generated correlation between the NVD and the quantized cavity field is quantified using the negativity. This study also investigates geometric phase and its dependence on the system parameters. The results show that this system holds great potential applications in quantum computation and quantum memory. Additionally, the features of the system can be controlled by the system parameters.

Controlling topological phases of matter with quantum light

Controlling the topological properties of quantum matter is a major goal of condensed matter physics. A major effort in this direction has been devoted to using classical light in the form of Floquet drives to manipulate and induce states with non-trivial topology. A different route can be achieved with cavity photons. Here we consider a prototypical model for topological phase transition, the one-dimensional Su-Schrieffer-Heeger model, coupled to a single mode cavity. We show that quantum light can affect the topological properties of the system, including the finite-length energy spectrum hosting edge modes and the topological phase diagram. In particular we show that depending on the lattice geometry and the strength of light-matter coupling one can either turn a trivial phase into a topological one or viceversa using quantum cavity fields. Furthermore, we compute the polariton spectrum of the coupled electron-photon system, and we note that the lower polariton branch disappears at the topological transition point. This phenomenon can be used to probe the phase transition in the Su-Schrieffer-Heeger model.

Enantiodiscrimination of chiral molecules via quantum correlation function.

We propose a method to realize enantiodiscrimination of chiral molecules based on quantum correlation function in a driven cavity-molecule system, where the chiral molecule is coupled with a quantized cavity field and two classical light fields to form a cyclic three-level model. According to the inherent properties of electric-dipole transition moments of chiral molecules, there is a π-phase difference in the overall phase of the cyclic three-level model for the left- and right-handed chiral molecules. Thus, the correlation function depends on this overall phase and is chirality-dependent. The analytical and numerical results indicate that the left- and right-handed chiral molecules can be discriminated by detecting quantum correlation function. Our work opens up a promising route to discriminate molecular chirality, which is an extremely important task in pharmacology and biochemistry.

Gaussian soft control for controlled-Z gate on superconducting qubits with unilateral external driving

Soft quantum control is a valid technique for highly selective interactions recently illustrated in Haase et al (2018 Phys. Rev. Lett. 121 050402), holding efficient resonant couplings among target levels while largely suppressing unwanted off-resonant contributions. Here we present a model for implementing a controlled-Z (CZ) gate in superconducting circuit quantum electrodynamics (QED) with two qubits being coupled to a microwave cavity. An external classical field that drives only one qubit, combined with the strong single-mode quantized cavity field dressing both qubits, is employed to induce the CZ gate between two qubits, and is also further tailored as a Gaussian soft control (GSC) to improve gate performances in various aspects. By contrast, we show that, with the same gate time, the CZ gate based on GSC can hold a higher fidelity, greater resilience to parameter errors, and stronger robustness against decoherence of system than that based on a rectangular pulse.

Dispersive Readout of Molecular Spin Qudits

We study the physics of a magnetic molecule described by a "giant" spin with multiple ($d > 2$) spin states interacting with the quantized cavity field produced by a superconducting resonator. By means of the input-output formalism, we derive an expression for the output modes in the dispersive regime of operation. It includes the effect of magnetic anisotropy, which makes different spin transitions addressable. We find that the measurement of the cavity transmission allows to uniquely determine the spin state of the qudits. We discuss, from an effective Hamiltonian perspective, the conditions under which the qudit read-out is a non-demolition measurement and consider possible experimental protocols to perform it. Finally, we illustrate our results with simulations performed for realistic models of existing magnetic molecules.

Influence of an External Classical Field on a ♢ Four-Level Atom Inside a Quantized Field

In this paper, we study the effect of detuning parameters and driven external classical field parameters on a quantum system consisting of a ♢-configuration four-level atom inside a quantized cavity field. Under some canonical conditional of dressed states, the exact solution of the Schrödinger equation is obtained. The occupation of atomic levels and statistical population inversion is studied. Our results show that the classical field parameter dissolved the collapse periods and increased the maximum bounds of the upper state, while decreasing the lower bounds of the lower state. The detuning parameters reduce the minimum bounds of atomic levels and their inversion. On the other hand, the linear entropy and l1 norm of coherence are employed to measure the temporal evolution of the mixedness and coherence. It is found that the driven classical field improves the temporal evolution of the mixedness and lower bounds of coherence. However, the detuning parameters have a destructive effect on the mixedness and lower bounds of coherence. The intensity of the external classical field is regarded as a control parameter with different values of detuning parameters.

Quantum entanglement in a four-partite hybrid system containing three macroscopic subsystems

The combination of different quantum systems may allow the exploration of the distinctive features of each system for the investigation of fundamental phenomena as well as for quantum technologies. In this work we consider a setup consisting of an atomic ensemble enclosed within a laser-driven optomechanical cavity, having the moving mirror further (capacitively) coupled to a low frequency LC circuit. This constitutes a four-partite optoelectromechanical quantum system containing three macroscopic quantum subsystems of a different nature, viz, the atomic ensemble, the massive mirror and the LC circuit. The quantized cavity field plays the role of an auxiliary system that allows the coupling of two other quantum subsystems. We show that for experimentally achievable parameters, it is possible to generate steady state bipartite Gaussian entanglement between pairs of macroscopic systems. In particular, we find under which conditions it is possible to obtain a reasonable amount of entanglement between the atomic ensemble and the LC circuit, systems that might be suitable for constituting a quantum memory and for quantum processing, respectively. For complementarity, we discuss the effect of the environmental temperature on quantum entanglement.

Enantiodetection of cyclic three-level chiral molecules in a driven cavity

We propose an enantio-detection method of chiral molecules in a cavity with external drive. The chiral molecules are coupled with a quantized cavity field and two classical light fields to form the cyclic three-level systems. The chirality-dependent cavity-assisted three-photon process in the three-level systems leads to the generation of intracavity photons. Simultaneously, the drive field also results in the chirality-independent process of the generation of intracavity photons. Based on the interference between the intracavity photons generated from these two processes, one can detect the enantiomeric excess of chiral mixture via monitoring the transmission rate of the drive field.

Quantum effects induced by two classical fields in a coherent cavity field containing two two-level atoms

The paper derives an exact solution for a two-qubit system coupling to a quantized cavity field driven by two different types of external fields when the cavity is initially in a coherent field state. The two-qubit quantum coherence via the Jensen–Shannon divergence and the two-qubit entanglement via the negativity are investigated under the effects of the physical parameters. The results are depicted that, the generated two-qubit effects depend on the external-qubit and the external-field detunings as well as the initial cavity coherent intensity. It is found that the increase of the parameters of the initial coherent states, the detuning between the cavity field and the external classical field, and the detuning between the qubit and the external classical fields are played a key role in the dynamics of the population inversion and the generated entropic qubit-cavity entanglement. The oscillation amplitudes of the atomic population can be improved when the classical-field detuning is equal to the qubit detuning, and they can be weakened dramatically when the qubit detuning is smaller than the classical-field detuning. The qubit-cavity entanglement can be improved when the classical-field detuning is larger than the qubit detuning, and vice versa. • An exact solution is derived for a two-qubit system coupling to a quantized cavity field driven by two different types of external fields. • Dynamics of population inversion and generated entropy qubit-cavity entanglement are explored under the initial states as well as the detunings. • Two-qubit quantum coherence via the Jensen–Shannon divergence and the two-qubit entanglement via the negativity are investigated.

Microwave multiphoton conversion via coherently driven permanent dipole systems

We investigate the multiphoton quantum dynamics of a leaking single-mode quantized cavity field coupled with a resonantly driven two-level system possessing permanent dipoles. The frequencies of the interacting subsystems are being considered very different, e.g., microwave ranges for the cavity and optical domains for the frequency of the two-level emitter, respectively. In this way, the emitter couples to the resonator mode via its diagonal dipole moments only. Furthermore, the generalized Rabi frequency resulting form the external coherent driving of the two-level subsystem is assumed as well different from the resonator's frequency or its multiples. As a consequence, this highly dispersive interaction regime is responsible for the cavity multiphoton quantum dynamics and photon conversion from optical to microwave ranges, respectively.

Ground state properties and infrared spectra of anharmonic vibrational polaritons of small molecules in cavities.

Recent experiments and theory suggest that ground state properties and reactivity of molecules can be modified when placed inside a nanoscale cavity, giving rise to strong coupling between vibrational modes and the quantized cavity field. This is commonly thought to be caused either by a cavity-distorted Born-Oppenheimer ground state potential or by the formation of light-matter hybrid states, vibrational polaritons. Here, we systematically study the effect of a cavity on ground state properties and infrared spectra of single molecules, considering vibration-cavity coupling strengths from zero up to the vibrational ultrastrong coupling regime. Using single-mode models for Li-H and O-H stretch modes and for the NH3 inversion mode, respectively, a single cavity mode in resonance with vibrational transitions is coupled to position-dependent molecular dipole functions. We address the influence of the cavity mode on polariton ground state energies, equilibrium bond lengths, dissociation energies, activation energies for isomerization, and on vibro-polaritonic infrared spectra. In agreement with earlier work, we observe all mentioned properties being strongly affected by the cavity, but only if the dipole self-energy contribution in the interaction Hamiltonian is neglected. When this term is included, these properties do not depend significantly on the coupling anymore. Vibro-polaritonic infrared spectra, in contrast, are always affected by the cavity mode due to the formation of excited vibrational polaritons. It is argued that the quantized nature of vibrational polaritons is key to not only interpreting molecular spectra in cavities but also understanding the experimentally observed modification of molecular reactivity in cavities.

Controllable and shortcut-based population transfers with a composite system of a nitrogen-vacancy electron spin and microwave photons

Optimal population transfer is of critical importance for quantum information processing. Here an efficient scheme is proposed for implementing controllable and shortcut-based population transfers with a nitrogen-vacancy (NV) electron spin and cavity photons. The electron spin is placed inside a setup of circuit quantum electrodynamics (QED). Under a suitable magnetic field bias, the ground state of electron spin constitutes an effective triplet. By means of the quantized cavity field and classical drivings, we obtain a $$\Delta $$ -configuration interaction within a composite three-state system. Based on the adjustable Rabi couplings, the shortcut-based population transfers can be performed controllably. Moreover, compared with the adiabatic counterparts, the operations assisted by counter-diabatic drivings need much shorter times and then are less susceptible to decoherence effects. Our scheme provides a promising avenue toward optimized transfer operations on NV center electron spins in circuit QED.

Theory of photon condensation in a spatially varying electromagnetic field

The realization of equilibrium superradiant quantum phases (photon condensates) in a spatially-uniform quantum cavity field is forbidden by a "no-go" theorem stemming from gauge invariance. We here show that the no-go theorem does not apply to spatially-varying quantum cavity fields. We find a criterion for its occurrence that depends solely on the static, non-local orbital magnetic susceptibility $\chi_{\rm orb}(q)$, of the electronic system (ES) evaluated at a cavity photon momentum $\hbar q$. Only 3DESs satisfying the Condon inequality $\chi_{\rm orb}(q)>1/(4\pi)$ can harbor photon condensation. For the experimentally relevant case of two-dimensional (2D) ESs embedded in quasi-2D cavities the criterion again involves $\chi_{\rm orb}(q)$ but also the vertical size of the cavity. We use these considerations to identify electronic properties that are ideal for photon condensation. Our theory is non-perturbative in the strength of electron-electron interaction and therefore applicable to strongly correlated ESs.

Double electromagnetically induced transparency windows in the [formula omitted]-type three-level atoms-assisted optomechanical system

We investigate electromagnetically induced transparency (EIT) in an optomechanical system that consists of a Λ-type three-level atomic medium confined inside an optical cavity with an oscillating mirror in the one end. The atoms are driven by a quantized field that acts as a control field of the EIT system and the quantized cavity field is known as a probe field. It can be seen double EIT windows separated by an absorption peak at the center of the EIT window in the output probe field. We analyse in detail effect of the photon numbers of the control and probe fields, the phonon number and the frequency of the oscillating mirror on the transparency windows. The results show that the width of transparency windows increases with the increase of the photon number of the control field and the phonon number of the oscillating mirror. Also, it is shown that the full width at half maximum (FWHM) of the absorption peaks changes with changing the above-mentioned parameters.

Dynamics of a nonlinear time-dependent two two-level atoms in a two-mode cavity

In this paper, we present some properties through two two-level atoms interacting with a two-mode quantized cavity field. We study this system in the presence of detuning parameter, Kerr nonlinearity, Stark shift, relative phase and intensity-dependent atoms-field coupling. Also, the coupling parameter is modulated to be time dependent. The exact solution of this model is given by using the Schrődinger equation when the atoms and the field are initially prepared in superposition states and coherent states, respectively. We employed the results to calculate some aspects such as linear entropy, total atomic inversion and cross-correlation function.