low-Q Cavity Research Articles

High-fidelity n-qubit quantum controlled-not gates on quantum-dot spins.

Realizing high-fidelity n-qubit quantum controlled-not gates is of critical significance. Applying quantum-dot (QD) spins as qubits, an (n - 1)-qubit control 1-qubit not gate and a 1-qubit control (n - 1)-qubit not gate is constructed. By utilizing the balanced condition, even under the condition of weak coupling, the circuit including the wave-form correctors and the balanced reflection condition of the cavity may effectively reduce the noise resulting from the unequal reflectance, so that the fidelity of each quantum gate operation can be increased to unity in theory. The operational complexity is further reduced, considering that low-Q cavities are used. In addition, the control gate of m-qubit control (n - m)-qubit can also be performed with a similar device diagram, only by changing the numbers of the control qubits and target qubits. These n-qubit controlled-not gates can help construct simpler quantum computing circuits that can be widely applied in quantum information processing.

A non-resonant approach for dielectric constant reconstructions via Newton iterations

In this study, a Newton–Raphson-based iterative method has been proposed to obtain dielectric constants accurately from measurements. The originalities of the approach lie in its applicability at non-resonant frequencies, which brings a significant experimental simplicity by avoiding critical coupling, expansion of available frequencies in different bands with the same cost-efficient low-Q (≈60) cavity. The direct problem involves either measuring power values inside a cavity (14.6 × 5 × 20.6) cm via a spectrum analyzer or simulating the complete setup via CST-MWS software at one of the non-resonant modes, 1.5 GHz. The solution to the inverse problem provides fastly converging results with an error rate of 1% for the unknown permittivities. The experiments were carried out using five different liquid samples even though the proposed technique does not have a limitation on solid materials. Applicability and the effectiveness of the introduced method is illustrated in detail and comparisons with the perturbation method is provided.

Optical noise-resistant nonreciprocal phonon blockade in a spinning optomechanical resonator.

A scheme of nonreciprocal conventional phonon blockade (PB) is proposed in a spinning optomechanical resonator coupled with a two-level atom. The coherent coupling between the atom and breathing mode is mediated by the optical mode with a large detuning. Due to the Fizeau shift caused by the spinning resonator, the PB can be implemented in a nonreciprocal way. Specifically, when the spinning resonator is driven from one direction, the single-phonon (1PB) and two-phonon blockade (2PB) can be achieved by adjusting both the amplitude and frequency of the mechanical drive field, while phonon-induced tunneling (PIT) occurs when the spinning resonator is driven from the opposite direction. The PB effects are insensitive to cavity decay because of the adiabatic elimination of the optical mode, thus making the scheme more robust to the optical noise and still feasible even in a low-Q cavity. Our scheme provides a flexible method for engineering a unidirectional phonon source with external control, which is expected to be used as a chiral quantum device in quantum computing networks.

High-specificity molecular sensing on an individual whispering-gallery-mode cavity: coupling-enhanced Raman scattering by photoinduced charge transfer and cavity effects.

Optical whispering-gallery-mode (WGM) cavities have gained considerable interest because of their unique properties of enhanced light-matter interactions. Conventional WGM sensing is based on the mechanisms of mode shift, mode broadening, or mode splitting, which requires a small mode volume and an ultrahigh Q-factor. Besides, WGM sensing suffers from a lack of specificity in identifying substances, and additional chemical functionalization or incorporation of plasmonic materials is required for achieving good specificity. Herein, we propose a new sensing method based on an individual WGM cavity to achieve ultrasensitive and high-specificity molecular sensing, which combines the features of enhanced light-matter interactions on the WGM cavity and the "fingerprint spectrum" of surface-enhanced Raman scattering (SERS). This method identifies the substance by monitoring the Raman signal enhanced by the WGM cavity rather than monitoring the variation of the WGM itself. Therefore, ultrasensitive and high-specificity molecular sensing can be accomplished even on a low-Q cavity. The working principles of the proposed sensing method were also systematically investigated in terms of photoinduced charge transfer, Purcell effect, and optical resonance coupling. This work provides a new WGM sensing approach as well as a strategy for the design of a high-performance SERS substrate by creating an optical resonance mode.

Структура и особенности автомодуляции сверхизлучательных состояний в асимметричном резонаторе Фабри-Перо

The dependence of the structure and stability of strongly asymmetric stationary states of a superradiant laser with a slightly asymmetric low-Q Fabry-Perot cavity on its length, reflection factors of mirrors, and pumping level is studied. The states are related to a self-consistent inhomogeneous half-wavelength population inversion grating. The possibility of the existence of two dynamic phase transitions from a stationary (monochromatic) state of this type to a nonstationary one is established: 1) a dissipative superradiant transition to a regime with a quasi-continuous lasing spectrum (in a weakly asymmetric cavity) and 2) a self-modulation transition to a regime with a discrete lasing spectrum. It is shown that the latter can be caused by excitation of both polariton and electromagnetic laser modes due to resonant Rabi oscillations of active centers with a sufficiently long phase relaxation time.

Strong dissipation induced coupling interaction between photons

Dissipation is used to achieve the coupling interaction between different cavities connected by a low-Q cavity. When the dissipative rate of the central cavity is enough large, vacuum Rabi oscillation can be found. We obtain the noise spectrum which may show the unique dynamics character of the investigated system. Under the condition of strong dissipation, non-zero entanglement between photons may be observed. We also discuss the effect of thermal noise on the dynamic evolution. The work will be helpful for manipulating photonic state in noisy environment.

Steady states of Λ-type three-level systems excited by quantum light with various photon statistics in lossy cavities

The interaction between quantum light and matter is being intensively studied for systems that are enclosed in high-Q cavities which strongly enhance the light–matter coupling. Cavities with low Q-factors are generally given less attention due to their high losses that quickly destroy quantum systems. However, bad cavities can be utilized for several applications, where lower Q-factors are required, e.g., to increase the spectral width of the cavity mode. In this work, we demonstrate that low-Q cavities can be beneficial for preparing specific electronic steady states when certain quantum states of light are applied. We investigate the interaction between quantum light with various statistics and matter represented by a Λ-type three-level system in lossy cavities, assuming that cavity losses are the dominant loss mechanism. We show that cavity losses lead to non-trivial electronic steady states that can be controlled by the loss rate and the initial statistics of the quantum fields. We discuss the mechanism of the formation of such steady states on the basis of the equations of motion and present both analytical expressions and numerical simulations for such steady states.

Поляритонный резонанс в автомодуляции асимметричного состояния сверхизлучающего лазера

Based on the numerical solution to the semiclassical Maxwell-Bloch equations in a one-dimensional model of a superradiant laser with a low-Q symmetric Fabry-Perot cavity, a comparative analysis of the spectrum of polariton modes of the linearized problem and the discrete spectrum of the of quasi-monochromatic generation with weak self-modulation under the condition of strong spontaneous mirror symmetry breaking of the counterpropagating electromagnetic waves, population inversion and polarization of an active medium is carried out. It is shown that the main frequencies of resonant self-modulation of a steady asymmetric superradiant phase state are close to the frequencies of polariton modes that are calculated in the linearized problem for the average level of the population inversion taken from the nonlinear problem and have small decay rates.

Coexistence of Coherent Pulses Formed by Superradiant and Quasi-Stationary Modes in a Laser with Low-Q Cavity

Coexistence of Coherent Pulses Formed by Superradiant and Quasi-Stationary Modes in a Laser with Low-Q Cavity

Single-atom maser with an engineered circuit for population inversion

We present a blueprint for a maser with a single three-level transmon superconducting artificial atom. The system can be pumped coherently via a two-photon process, and to achieve high population inversion, the relaxation rate of the metastable state is increased via an auxiliary low-Q cavity coupled to a transition between the transmon excited states. We show numerically that such a maser can operate both in the intermediate coupling regime with super-Poissonian photon statistics and in the strong coupling regime, where the statistics is sub-Poissonian. For the former, the maser exhibits thresholdless behavior and for the latter, there is a well-defined pumping threshold. A useful side-effect of the auxiliary resonator is that it allows to overcome the photon blockade effect for the pump, which would otherwise prevent high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.

Зависимость спектра генерации и синхронизации мод от ширины запрещенной фотонной зоны в гетеролазерах класса С с распределенной обратной связью волн в резонаторе Фабри-Перо

Based on the numerical solution to the nonlinear Maxwell-Bloch equations, the joint implementation of active (parametric) and passive (coherent) mode locking for a class C heterolaser with a low-Q combined Fabry-Perot cavity in the presence of an effective distributed feedback of counter-propagating waves is demonstrated. It is shown that the multiplicity of the spectral width of the photonic band gap of the cavity to the intermode spacing far from this zone contributes to the effective phasing of quasi-monochromatic quasi-equidistant modes, thus making it possible a phenomenon of parametric coherent self-mode-locking. A number of examples are used to demonstrate typical properties of a quasi-periodic sequence of soliton-like pulses generated in the found regime, which does not require external modulation of the pump or laser parameters, or the placement of a fast-saturating absorber in it.

Parametric effect in a superradiant laser with self-mode-locking

Based on numerical simulation of the nonstationary working of a CW superradiant laser with a low-Q combined Fabry-Perot cavity with distributed feedback of waves, we describe a parametric mechanism of self-mode-locking caused by beats of two superradiant modes with a period half that of the cavity round-trip period and supporting the formation of a soliton of the electromagnetic field inside the cavity without using any additional mode-locking technique.

Coexistence of Coherent Pulses Formed by Superradiant and Quasistationary Modes in a Laser With Low-Q Cavity

Coexistence of Coherent Pulses Formed by Superradiant and Quasistationary Modes in a Laser With Low-Q Cavity

One-way steering of the optical fields with respect to the low-Q cavity via the thermal noise

We show that thermal noise could play a positive role in generating one-way Einstein–Podolsky–Rosen (EPR) steering of two cavity fields dispersively interacting with a single four-level atom, each of which is independently coupled to a thermal reservoir. In the low-Q and weak Raman transition regimes, two output fields exhibit asymmetric EPR steering and the steering direction could be easily controlled by adjusting the mean photon numbers of the thermal reservoirs and the decay rates of cavities. Striking features are present in our scheme. First, one-way EPR steering is achieved by using the couplings of the cavities with the heat baths, which sheds light on the quantum state manipulation in the presence of decoherence. Second, the obtainable EPR steering occurs between the cavity fields in the low-Q regime, which relaxes the constraints on the use of good cavities and so makes our scheme more practical. Third, the correlation properties of the output modes are considered, which can be measured more conveniently and will be more applicable to implement a range of quantum information processing.

One-way steering of the optical fields with respect to the low-Q cavity via the thermal noise

We show that thermal noise could play a positive role in generating one-way Einstein–Podolsky–Rosen (EPR) steering of two cavity fields dispersively interacting with a single four-level atom, each of which is independently coupled to a thermal reservoir. In the low-Q and weak Raman transition regimes, two output fields exhibit asymmetric EPR steering and the steering direction could be easily controlled by adjusting the mean photon numbers of the thermal reservoirs and the decay rates of cavities. Striking features are present in our scheme. First, one-way EPR steering is achieved by using the couplings of the cavities with the heat baths, which sheds light on the quantum state manipulation in the presence of decoherence. Second, the obtainable EPR steering occurs between the cavity fields in the low-Q regime, which relaxes the constraints on the use of good cavities and so makes our scheme more practical. Third, the correlation properties of the output modes are considered, which can be measured more conveniently and will be more applicable to implement a range of quantum information processing.

Ultra-broadband metamaterial absorber in long wavelength Infrared band based on resonant cavity modes

A wavelength-selective, ultrathin, broadband infrared metal–insulator–metal (MIM) absorber with multi-sized Ti–Ge cubes is proposed. By flexibly combining different sizes of Ti–Ge cubes, stacking upward and reasonably filling the border, all the resulting 3 structures that we propose show an average absorptivity of at least 90% over a wide spectral range in the infra-red, extending from 6. 3μm to 14.8μm. The absorptivity is further increased up to 99% when considering narrower spectral ranges such as 7.96-8.34μm and 11.02-11.75μm wavebands, which is superior than the previous work in long wavelength infrared band based on the MIM structure. Those characteristics vary depending on the 3 designs considered and studied in this work: single-layer structure, double-layer structure and modified structure. The intrinsic strong energy dissipation caused by highly lossy metal Ti (here Titanium) and excited low-Q cavity modes are key factors contributing to such efficient broadband absorption. The polarization and angle insensitivity are demonstrated by analysing the absorption performance with oblique incidences for both transverse electric wave (TE) and transverse magnetic wave (TM). Moreover, flexible combinations of different resonators allow trade-offs between the absorption bandwidth and the absorbance, which makes the operating waveband of the metamaterial absorber adjustable through proper design. The proposed broadband absorbers have many potential applications, including microbolometers, thermal emitters, and plasmonic sensors.

Error-detected N-photon cluster state generation based on the controlled-phase gate using a quantum dot in an optical microcavity

We propose a scheme for error-detected generation of an N-photon cluster state with a quantum dot (QD) embedded in a single-sided optical microcavity (QD-cavity system). The basic structure of this scheme is an error-detected controlled-phase (C-phase) gate on the hybrid electron-photon system. In this scheme, the fidelity of N-photon cluster state generation can be reached unity even if low-Q cavity and cavity leakage are considered. By using error detecting, the generation of an N-photon cluster state can be performed by repeating until success, which also leads to a high success probability, compared with other schemes assisted by the QD-cavity system. The error-detected generation of an N-photon cluster state in the highly controllable way may benefit on the quantum network in the future.

Light Scattering from Solid-State Quantum Emitters: Beyond the Atomic Picture.

Coherent scattering of light by a single quantum emitter is a fundamental process at the heart of many proposed quantum technologies. Unlike atomic systems, solid-state emitters couple to their host lattice by phonons. Using a quantum dot in an optical nanocavity, we resolve these interactions in both time and frequency domains, going beyond the atomic picture to develop a comprehensive model of light scattering from solid-state emitters. We find that even in the presence of a low-Q cavity with high Purcell enhancement, phonon coupling leads to a sideband that is completely insensitive to excitation conditions and to a nonmonotonic relationship between laser detuning and coherent fraction, both of which are major deviations from atomlike behavior.

On the Asymmetric Generation of a Superradiant Laser with a Symmetric Low-Q Cavity

On the basis of numerical solution to the Maxwell–Bloch equations within the one-dimensional two-level model of a superradiant laser with a symmetric cavity in which the photon lifetime is less than the incoherent relaxation time of the optical-dipole oscillations of active centers, the phenomenon of the spontaneous asymmetric generation of counter-propagating waves under continuous uniform pumping of the active medium is revealed. It is shown that the observed symmetry breaking of the spatial profiles of counter-propagating waves of the electromagnetic field and, the polarization and inversion of the population of active-medium levels in the case of a small inhomogeneous broadening of the spectral line of its working transition occurs due to the asymmetric half-wave nonlinear grating of inversion of the energy-level population produced by these waves.

Robust hybrid hyper-controlled-not gates assisted by an input-output process of low-Q cavities.

The two or more degrees of freedoms (DOFs) of photon systems are very useful in hyperparallel photonic quantum computing to accomplish more quantum logic gate operations with less resource, and depress photonic dissipation noise in quantum information processing. We present some flexible and adjustable schemes for hybrid hyper-controlled-not (hyper-CNOT) gates assisted by low-Q cavities, on the two-photon systems in both the spatial-mode and the polarization DOFs. These hybrid spatial-polarization hyper-CNOT gates consume less quantum resource and are more robust against photonic dissipation noise, compared with the integration of two cascaded CNOT gates in one DOF. Besides, simultaneous counter-propagation of two photons economize extremely the operation time in the whole process of our schemes. Moreover, these quantum logic gates are more feasible for fast quantum operations in the weak-coupling region of the low-Q cavities with current experimental technology, which are much different from strong-coupling cases of the high-Q ones.