Leaky Cavity Research Articles

Leaky cavity modes in metasurfaces: a route to low-loss wideband anomalous dispersion

Metasurfaces have provided unprecedented degrees of freedom in manipulating electromagnetic waves upon interfaces. In this work, we first explore the condition of wide operating bandwidth in the view of reflective scheme, which indicates the necessity of anomalous dispersion. To this end, the leaky cavity modes (LCMs) in the meta-atom are analyzed and can make effective permittivity inversely proportional to frequency. Here we employ the longitudinal Fabry–Perot (F-P) resonances and transverse plasmonic resonances to improve the LCMs efficiency. It is shown that the order of F-P resonance can be customized by the plasmonic modes, that is, the F-P cavity propagation phase should match the phase delay of surface currents excited on the meta-atom. The nth order F-P resonance will multiply the permittivity by a factor of n, allowing larger phase accumulation with increasing frequencies and forming nonlinear phase distribution which can be applied in weak chromatic-aberration focusing design. As a proof-of-concept, we demonstrate a planar weak chromatic-aberration focusing reflector with a thickness of λ0/9 at 16.0–21.0 GHz. This work paves a robust way to advanced functional materials with anomalous dispersion and can be extended to higher frequencies such as terahertz, infrared, and optical frequencies.

Highly Efficient Single-Exciton Strong Coupling with Plasmons by Lowering Critical Interaction Strength at an Exceptional Point.

The single-exciton strong coupling with the localized plasmon mode (LPM) at room temperature is highly desirable for exploiting quantum technology. However, its realization has been a very low probability event due to the harsh critical conditions, severely compromising its application. Here, we present a highly efficient approach for achieving such a strong coupling by reducing the critical interaction strength at the exceptional point based upon the damping inhibition and matching of the coupled system, instead of enhancing the coupling strength to overcome the system's large damping. Experimentally, we compress the LPM's damping linewidth from about 45nm to about 14nm using a leaky Fabry-Perot cavity, a good match to the excitonic linewidth of about 10nm. This method dramatically relaxes the harsh requirement in mode volume by more than an order of magnitude and allows a maximum direction angle of the exciton dipole relative to the mode field of up to around 71.9°, significantly improving the success rate of achieving the single-exciton strong coupling with LPMs from about 1% to about 80%.

All-epitaxial resonant cavity enhanced long-wave infrared detectors for focal plane arrays

We demonstrate a monolithic all-epitaxial resonant-cavity architecture for long-wave infrared photodetectors with substrate-side illumination. An nBn detector with an ultra-thin (t≈350 nm) absorber layer is integrated into a leaky resonant cavity, formed using semi-transparent highly doped (n++) epitaxial layers, and aligned to the anti-node of the cavity's standing wave. The devices are characterized electrically and optically and demonstrate an external quantum efficiency of ∼25% at T=180 K in an architecture compatible with focal plane array configurations.

Quantumness and speedup limit of a qubit under transition-frequency modulation

Controlling and maintaining quantum properties of an open quantum system along its evolution is essential for both fundamental and technological aims. We assess the capability of a frequency-modulated qubit embedded in a leaky cavity to exhibit enhancement of its dynamical quantum features. The qubit transition frequency is sinusoidally modulated by an external driving field. We show that a properly optimized quantum witness effectively identifies quantum coherence protection due to frequency modulation while a standard quantum witness fails. We also find an evolution speedup of the qubit through proper manipulation of the modulation parameters of the driving field. Importantly, by introducing a new figure of merit Rg, we discover that the relation between Quantum Speed Limit Time (QSLT) and non-Markovianity depends on the system initial state, which generalizes previous connections between these two dynamical features. The frequency-modulated qubit model thus manifests insightful dynamical properties with potential utilization against decoherence.

Quantum Speed Limit for a Moving Qubit inside a Leaky Cavity

The quantum speed limit (QSL) is a theoretical lower bound of the time required for a quantum system to evolve from an arbitrary initial state to its orthogonal counterpart. This figure can be used to characterize the dynamics of open quantum systems, including non-Markovian maps. In this paper, we investigate the QSL time for a model that consists of a single qubit moving inside a leaky cavity. Notably, we show that for both weak and strong coupling regimes, the QSL time increases while we boost the velocity of the qubit inside the leaky cavity. Moreover, it is observed that by increasing the qubit velocity, the speed of the evolution tends to a constant value, and the system becomes more stable. The results provide a better understanding of the dynamics of atom-photon couplings and can be used to enhance the controllability of quantum systems.

Robust Control Performance for Open Quantum Systems

Robust performance of control schemes for open quantum systems is investigated under classical uncertainties in the generators of the dynamics and nonclassical uncertainties due to decoherence and initial state preparation errors. A formalism is developed to measure performance based on the transmission of a dynamic perturbation or initial state preparation error to the quantum state error. This makes it possible to apply tools from classical robust control, such as structured singular value analysis. A difficulty arising from the singularity of the closed-loop Bloch equations for the quantum state is overcome by introducing the #-inversion lemma, a specialized version of the matrix inversion lemma. Under some conditions, this guarantees continuity of the structured singular value at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$s = 0$</tex-math></inline-formula> . Additional difficulties occur when symmetry gives rise to multiple open-loop poles, which under symmetry-breaking unfold into single eigenvalues. The concepts are applied to systems subject to pure decoherence and a general dissipative system example of two qubits in a leaky cavity under laser driving fields and spontaneous emission. A nonclassical performance index, steady-state entanglement quantified by the concurrence, a nonlinear function of the system state, is introduced. Simulations confirm a conflict between entanglement, its log-sensitivity and stability margin under decoherence.

Low-Complexity 3D InISAR Imaging Using a Compressive Hardware Device and a Single Receiver.

An Interferometric Inverse SAR system is able to perform 3D imaging of non-cooperative targets by measuring their responses over time and through several receiving antennas. Phase differences between signals acquired with a spatial diversity in vertical or horizontal directions are used to localize moving scatterers in 3D. The use of several receiving channels generally results into a costly and complex hardware solution, and this paper proposes performing this multichannel acquisition using a single receiver and a hardware compressive device, based on a chaotic cavity which simultaneously multiplexes in the spectral domain signals acquired over different antennas. The radar responses of the scene are encoded in the spectral domain onto the single output of a leaky chaotic cavity, and can be retrieved by solving an inverse problem involving the random transfer matrix of the cavity. The applicability of this compressed sensing approach for the 3D imaging of a non-cooperative target using low-complexity hardware is demonstrated using both simulations and measurements. This study opens up new perspectives to reduce the hardware complexity of high-resolution ISAR systems.

Witnessing entanglement between two two-level atoms moving inside a leaky cavity under classical control

Based on the quantum memory-assisted entropic uncertainty relation (QMA-EUR), we investigate the Markovian and non-Markovian dynamics of entanglement witness in a two-atom system that asymmetrically are coupled to a leaky cavity with two-photon relaxation. The atoms are two-level systems, they move inside the cavity and interact with a classical driving laser field. We discuss in detail the effects of the translational movement of the atoms, classical driving field and atom-cavity coupling on the protection of entanglement witness. Our results show that with a regular increase in the intensity of the classical driving field, the entanglement region witnessed by lower bound of QMA-EUR increases and the time of entanglement witness gets longer. In the Markovian regime, we find that quantum entanglement between the moving atoms can be witnessed for a longer time by increasing the velocity of the atoms. However, in the non-Markovian regime, higher speeds are required to witness entanglement over long time intervals. In addition, we conclude that the entanglement region witnessed by the lower bound of QMA-EUR can be protected in both the symmetrical and asymmetrical atom-cavity coupling regimes. In the asymmetrical regime, a better protection can be achieved when the memory atom is coupled to the cavity field stronger than the other atom.

Witnessing entanglement between two two-level atoms coupled to a leaky cavity via two-photon relaxation

Witnessing entanglement between two two-level atoms coupled to a leaky cavity via two-photon relaxation

Respiratory Strategies in Relation to Ecology and Behaviour in Three Diurnal Namib Desert Tenebrionid Beetles.

Simple SummaryThe Namib Desert has a large diversity of darkling beetle species. All these beetles are flightless and feed on plant detritus. The aim of this study was to investigate whether the respiration strategies used by these beetles are linked to their ecology and behaviour. Three beetle species, which are all active during the day, in direct sunshine, running across the sand surface, but found in different parts of the desert, were chosen for this study. All three beetle species used intermittent breathing. They held their breath for several minutes and released CO2 in pulses. The large beetle species, which runs rapidly on the dune slip face when air temperatures are high, used evaporative cooling to prevent over-heating. The water used in the cooling comes from their respiratory surfaces and is replenished from metabolising food and drinking water droplets left on vegetation after a fog event. The two smaller beetle species, which inhabit the gravel plains, limit the area of the respiratory surface exposed to the atmosphere, which reduces body water loss. These two beetle species are not known to drink water, and thus have a greater need to conserve their body water.The respiratory physiology of three diurnal ultraxerophilous tenebrionid beetles inhabiting either the dune slipface or gravel plain in the Namib Desert was investigated. The role of the mesothoracic spiracles and subelytral cavity in gas exchange was determined by flow-through respirometry. All three species exhibited the discontinuous gas exchange cycles with a distinct convection based flutter period and similar mass specific metabolic rates. There was variation in their respiration mechanics that related to the ecology of the species. The largest beetle species, Onymacris plana, living on the dune slipface, has a leaky subelytral cavity and used all its spiracles for gas exchange. Thus, it could use evaporative cooling from its respiratory surface. This species is a fog harvester as well as able to replenish water through metabolising fats while running rapidly. The two smaller species inhabiting the gravel plains, Metriopus depressus and Zophosis amabilis, used the mesothoracic spiracles almost exclusively for gas exchange as well as increasing the proportional length of the flutter period to reduce respiratory water loss. Neither species have been reported to drink water droplets, and thus conserving respiratory water would allow them to be active longer.

Switchability of multimodal optical phases in a leaky and nonlinear quantum cavity

In the present report, the question of U(1) symmetry breaking in a system of atoms and electromagnetic fields, interacting inside a leaky cavity, filled with a nonlinear medium, is addressed. In particular, the ${Z}_{2}$ discrete symmetry of the system and the emergence of optical phases are fully discussed. For the nonlinearity of a general order, with an electromagnetic field of any number of modes, conditions under which the resulting field-field interactions destroy the U(1) (and ${Z}_{2}$) symmetry are determined. We then apply the theory to the case of a collection of two-level atoms and three electromagnetic modes. Taking one of the fields as a classically adjustable pumping one, it is demonstrated that the quantized field-field coupling profoundly depends upon the pump field strength. The presence of two competing phenomena, namely, the cavity photonic dissipation and nonlinearity, is shown to lead the system towards steady behavior. The steady-state solutions to the atomic population and field quadratures exhibit the normal and superradiant phases, depending on the strengths of pumping field and atom-field couplings. The conditions for the stability of such steady-state solutions are also discussed in detail. A notable result of the present article is that by adjusting the parameters involved in the system one can switch from the normal to electric and/or magnetic superradiant phases.

Chaotic spin-photonic quantum states in an open periodically modulated cavity.

When applied to dynamical systems, both classical and quantum, time periodic modulations can produce complex non-equilibrium states which are often termed "chaotic." Being well understood within the unitary Hamiltonian framework, this phenomenon is less explored in open quantum systems. Here, we consider quantum chaotic states emerging in a leaky cavity when the intracavity photonic mode is coherently pumped with the pumping intensity varying periodically in time. We show that a single spin when placed inside the cavity and coupled to the mode can moderate transitions between regular and chaotic regimes-that are identified by using quantum Lyapunov exponents or features of photon emission statistics-and thus can be used to control the degree of chaos.

Quantum-memory-assisted entropic uncertainty relation with moving quantum memory inside a leaky cavity

Uncertainty principle has a fundamental role in quantum theory. This principle states that it is not possible to measure two incompatible observers simultaneously. The uncertainty principle is expressed logically in terms of standard deviation of the measured observables. In quantum information, it has been shown that the uncertainty principle can be expressed by means of Shannon’s entropy. Entropic uncertainty relation can be improved by considering an additional particle as the quantum memory. In the presence of quantum memory the entropic uncertainty relation is called quantum-memory-assisted entropic uncertainty relation. In this work, we will consider the case in which the quantum memory moves inside the leaky cavity. We will show that by increasing the velocity of the quantum memory, the entropic uncertainty lower bound is decreased.

Exact entanglement dynamics mediated by leaky optical cavities

We present a quantum-state-diffusion equation to characterize the dynamics of a generic atomic system due to the coupling to a leaky cavity mode. As quantum resources, the population, the coherence and even the entanglement of the system would gradually leak out of the cavity. The effect from the leakage of the cavity-mode to the uncontrollable degrees of freedom, e.g. environment, is however not always negative to particular applications of these quantum resources. We investigate the competition between these two mechanisms in the framework of the non-Markovian open-quantum-system dynamics, where the leaky mode serves as a general two-layer bosonic environment. Numerical calculations based on our non-perturbative approach reveal a generation of quantum entanglement in the qubit system due to the coupling to a resonant leaky cavity.

Validating and controlling quantum enhancement against noise by the motion of a qubit

Experimental validation and control of quantum traits for an open quantum system are important for any quantum information purpose. We consider a traveling atom qubit as a quantum memory with adjustable velocity inside a leaky cavity, adopting a quantum witness as a figure of merit for quantumness assessment. We show that this model constitutes an inherent physical instance where the quantum witness does not work properly if not suitably optimized. We then supply the optimal intermediate blind measurements which make the quantum witness a faithful tester of quantum coherence. We thus find that larger velocities protect quantumness against noise, leading to lifetime extension of hybrid qubit-photon entanglement and to higher phase estimation precision. Control of qubit motion thus reveals itself as a quantum enhancer.

Quantumness and memory of one qubit in a dissipative cavity under classical control

Hybrid quantum–classical systems constitute a promising architecture for useful control strategies of quantum systems by means of a classical device. Here we provide a comprehensive study of the dynamics of various manifestations of quantumness with memory effects, identified by non-Markovianity, for a qubit controlled by a classical field and embedded in a leaky cavity. We consider both Leggett–Garg inequality and quantum witness as experimentally-friendly indicators of quantumness, also studying the geometric phase of the evolved (noisy) quantum state. We show that, under resonant qubit-classical field interaction, a stronger coupling to the classical control leads to enhancement of quantumness despite a disappearance of non-Markovianity. Differently, increasing the qubit-field detuning (out-of-resonance) reduces the nonclassical behavior of the qubit while recovering non-Markovian features. We then find that the qubit geometric phase can be remarkably preserved irrespective of the cavity spectral width via strong coupling to the classical field. The controllable interaction with the classical field inhibits the effective time-dependent decay rate of the open qubit. These results supply practical insights towards a classical harnessing of quantum properties in a quantum information scenario.

Hybrid membrane resonators with fluid permeable cavity

We report the design and the experimental realization of perfect absorption of acoustic waves by a hybrid membrane resonator with air permeable membranes and demonstrate that hybrid membrane resonators with a leaky cavity can also achieve perfect absorption. We further increase the leakage of the cavity by opening small holes on the back wall of the cavity and demonstrate how the high absorption of the device could be restored by changing the cavity volume. The device so created has one surface being very low reflection and the other being high reflection, while maintaining good transmission, making it a good candidate for devices with a large Willis coefficient as well.

Dicke time crystals in driven-dissipative quantum many-body systems

The Dicke model—a paradigmatic example of superradiance in quantum optics—describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system’s dynamics is captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light–matter coupling can lead to time-crystalline-like behavior of the collective spin (Gong et al 2018 Phys. Rev. Lett. 120 040404). In this work, we investigate whether such a Dicke time crystal (TC) is stable to perturbations that explicitly break the mean-field solvability of the conventional Dicke model. In particular, we consider the addition of short-range interactions between the atoms which breaks the collective coupling and leads to complex many-body dynamics. In this context, the interplay between periodic driving, dissipation and interactions yields a rich set of dynamical responses, including long-lived and metastable Dicke-TCs, where losses can cool down the many-body heating resulting from the continuous pump of energy from the periodic drive. Specifically, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the coupling strength, suggesting the possible existence of stable dynamical order in a driven-dissipative quantum many-body system. These findings illustrate the rich nature of novel dynamical responses with many-body character in quantum optics platforms.

Dicke time crystals in driven-dissipative quantum many-body systems

The Dicke model—a paradigmatic example of superradiance in quantum optics—describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system's dynamics is captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light–matter coupling can lead to time-crystalline-like behavior of the collective spin (Gong et al 2018 Phys. Rev. Lett. 120 040404). In this work, we investigate whether such a Dicke time crystal (TC) is stable to perturbations that explicitly break the mean-field solvability of the conventional Dicke model. In particular, we consider the addition of short-range interactions between the atoms which breaks the collective coupling and leads to complex many-body dynamics. In this context, the interplay between periodic driving, dissipation and interactions yields a rich set of dynamical responses, including long-lived and metastable Dicke-TCs, where losses can cool down the many-body heating resulting from the continuous pump of energy from the periodic drive. Specifically, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the coupling strength, suggesting the possible existence of stable dynamical order in a driven-dissipative quantum many-body system. These findings illustrate the rich nature of novel dynamical responses with many-body character in quantum optics platforms.

Classical-driving-assisted coherence dynamics and its conservation**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675115, 11204156, 11574178, and 11304179), the Science and Technology Plan Projects of Shandong University, China (Grant No. J16LJ52), and the Natural Science Foundation of Shandong Province, China (Grant No. ZR2016AP09).

We investigate the quantum coherence and quantum entanglement dynamics of a classical driven single atom coupled to a single-mode cavity. It is shown that the transformation between the atomic coherence and the atom-field entanglement exists, and can be improved by adjusting the classical driving field. The joint evolution of two identical single-body systems is also studied. The results show the quantum coherence transfers among composite subsystems, and the coherence conservation of composite subsystems is obtained. Moreover, the classical driving field can be used to suppress the decay of the coherence and entanglement, owing to considering the leaky cavity. The non-Markovian dynamics of the system is also discussed finally.