Cavity Decay Rate Research Articles

Monitoring the Energy of a Cavity by Observing the Emission of a Repeatedly Excited Qubit.

The number of excitations in a large quantum system (harmonic oscillator or qudit) can be measured in a quantum nondemolition manner using a dispersively coupled qubit. It typically requires a series of qubit pulses that encode various binary questions about the photon number. Recently, a method based on the fluorescence measurement of a qubit driven by a train of identical pulses was introduced to track the photon number in a cavity, hence simplifying its monitoring and raising interesting questions about the measurement backaction of this scheme. A first realization with superconducting circuits demonstrated how the average number of photons could be measured in this way. Here we present an experiment that reaches single-shot photocounting and number tracking owing to a cavity decay rate 4 orders of magnitude smaller than both the dispersive coupling rate and the qubit emission rate. An innovative notch filter and pogo-pin-based galvanic contact makes possible these seemingly incompatible features. The qubit dynamics under the pulse train is characterized. We observe quantum jumps by monitoring the photon number via the qubit fluorescence as photons leave the cavity one at a time. Additionally, we extract the measurement rate and induced dephasing rate and compare them to theoretical models. Our method could be applied to quantum error correction protocols on bosonic codes or qudits.

Ground-state cooling of a mechanical oscillator by a noisy environment

Dissipation and the accompanying fluctuations are often seen as detrimental for quantum systems since they are associated with fast relaxation and loss of phase coherence. However, it has been proposed that a pure state can be prepared if external noise induces suitable downwards transitions, while exciting transitions are blocked. We demonstrate such a refrigeration mechanism in a cavity optomechanical system, where we prepare a mechanical oscillator in its ground state by injecting strong electromagnetic noise at frequencies around the red mechanical sideband of the cavity. The optimum cooling is reached with a noise bandwidth smaller than but on the order of the cavity decay rate. At higher bandwidths, cooling is less efficient as suitable transitions are not effectively activated. In the opposite regime where the noise bandwidth becomes comparable to the mechanical damping rate, damping follows the noise amplitude adiabatically, and the cooling is also suppressed.

Generation of entanglement and quantum steering via Josephson parametric amplifier in a dual cavity-magnon system

In the two microwave (MW) cross-shaped cavity magnon system, we describe a method to produce multipartite entanglement and quantum steering. To achieve squeezed states of the magnons, a Josephson parametric amplifier (JPA) creates a squeezed vacuum field that drives the two cavities. We theoretically demonstrate that the cavity-cavity entanglement can be generated at the resonance point, however, increasing the cavity and magnon decay rates generate the cavity-magnon entanglement. By changing the squeezing parameter and increasing the decay rates, we can transfer the cavity-cavity entanglement to cavity-magnon entanglement. Furthermore, the cavity-cavity entanglement (survive up to 2.8 K) was not only found to be much stronger but also more robust as compared to cavity-magnon entanglement (survive up to 0.4 K). More importantly, the genuine photon-magnon-photon tripartite entanglement could be achieved, which is robust against thermal fluctuations and depends strongly on the squeezing parameter. Furthermore, for the current dual cavity-magnon system, two-way quantum steering is found when the optomagnonical couplings are equal. The current study offers a straightforward and practical method for achieving multipartite quantum correlations.

Second-Order Sidebands and Group Delays in Coupled Optomechanical Cavity System with a Cubic Nonlinear Harmonic Oscillator

The generation of second-order sidebands and its associated group delay is an important subject in optical storage and switch. In this work, the efficiency of second-order sideband generation in a coupled optomechanical cavity system with a cubic nonlinear harmonic oscillator is theoretically investigated. It is found that the efficiency of second-order sideband generation can be effectively enhanced with the decrease in decay rate of optomechanical cavity, the increase in coupling strength between two cavities and the power of probe field. The slow light effect (i.e., positive group delay) is also observed in the proposed optomechanical cavity system, and can be controlled with the power of control field.

Gain of a High-Impedance Cavity Coupled to Strongly Driven Semiconductor Quantum Dots

The architecture of artificial atoms coupled to superconducting cavities allows the study of light-matter interactions and intriguing phenomena such as cavity gain implying photon generation. Here, we integrate a high-impedance cavity with a double quantum dot (DQD) in GaAs/(Al,Ga)As heterostructures, achieving a considerable DQD-cavity coupling strength and a relatively small cavity decay rate. By applying a strong drive to the DQD, we realize a population inversion and observe the cavity amplitude gain in multiple regions in the measured Landau-Zener-St\"uckelberg-Majorana interference pattern. We further systematically investigate the dependence of cavity gain on the driving frequency and tunnel coupling strength of the DQD. The results show that the cavity gain is tunable, with a maximum value of approximately $1.16$ in the measured range. Our experimental results are in good agreement with theoretical simulations and may provide an opportunity to implement on-chip microwave sources or microwave amplifiers in a controllable way.

Collapse-revival and stability of magnon-superconducting qubit entanglement in a tripartite hybrid cavity system

In this paper we pay our attention to the generation and manipulation of bipartite entanglement in a hybrid cavity system which is comprised of cavity microwave photons, a magnon and a superconducting qubit. To achieve the purpose of paper, at first, the time-independent effective Hamiltonian of the system is derived with considering some assumptions, and then the system solution is obtained via solving the Lindblad master equation. At last, the bipartite magnon-superconducting qubit entanglement is quantitatively analyzed using negativity, as a suitable measure of bipartite entanglement. The numerical simulations obviously show that, by adjusting system parameters, collapse-revival behavior of the entanglement can be apparently observed, and by appropriate choice of thermal occupation photon number and cavity decay rate, quasi-stable, even stable with significant degrees of entanglement are accessible. Our results indicate that, such a hybrid cavity system considered here can be used for studying large-scale quantum phenomena which has a crucial role in quantum information science and technologies.

Controllable Fano-type optical response and four-wave mixing via magnetoelastic coupling in an opto-magnomechanical system

We analytically investigate the Fano-type optical response and the four-wave mixing (FWM) process by exploiting the magnetoelasticity of a ferromagnetic material. The deformation of the ferromagnetic material plays the role of mechanical displacement, which is simultaneously coupled to both optical and magnon modes. We report that the magnetostrictively induced displacement leads to realization of Fano profiles in the output field and is effectively well-tuned through adjusting the system parameters, such as effective magnomechanical coupling, magnon detuning, and cavity detuning. It is found that the magnetoelastic interaction also gives rise to the FWM phenomenon. The number of the FWM signals mainly depends upon the effective magnomechanical coupling and the magnon detuning. Moreover, the FWM spectrum exhibits suppressive behavior upon increasing (decreasing) the magnon (cavity) decay rate. The present scheme will open new perspectives in highly sensitive detection and quantum information processing.

Microwave detection of gliding Majorana zero modes in nanowires

We study a topological superconducting nanowire that hosts gliding Majorana zero modes in the presence of a microwave cavity field. We show that the cavity decay rate depends on both the parity encoded by the Majorana zero modes and their motion, in the absence of any direct overlap of their wave functions. That is because the extended bulk states that overlap with both Majorana states facilitate their momentum-resolved microwave spectroscopy, with the gliding acting to modify the interference pattern via a momentum boost. Moreover, we demonstrate that these nonlocal effects are robust against moderate disorder in the chemical potential, and we confirm the numerical calculations with an analytical low-energy model. Our approach offers an alternative to tunneling spectroscopy to probe nonlocal features associated with the Majorana zero modes in nanowires.

Entanglement of mechanical modes in a doubly resonant optomechanical cavity of a correlated emission laser

We explore the extent of the induced entanglement of the mechanical modes that can be attributed to the transfer of coherence from two-mode cavity radiation in a doubly resonant optomechanical cavity. It is expected that this scheme can support a generation of mechanical oscillations with a robust degree of entanglement combined with significant controllability. The entanglement is found to be sensitive to the specific choices of the frequencies of the bichromatic drive laser. It also turns out that the degree of entanglement would be enhanced with increasing rates of injection of the atoms but with decreasing initial lengths of a doubly resonant cavity and atomic decay rates. In addition, the entanglement is found to behave qualitatively in the same way for the measures of entanglement we have applied. Since the scheme we considered can possibly be implemented with current technology and allows the quantum features of cavity radiation to be accessible for application, we anticipate that it can be utilized in the realization of continuous-variable quantum information processing.

Enhancing the force sensitivity of a squeezed light optomechanical interferometer.

Application of frequency-dependent squeezed vacuum improves the force sensitivity of an optomechanical interferometer beyond the standard quantum limit by a factor of e-r, where r is the squeezing parameter. In this work, we show that the application of squeezed light along with quantum back-action nullifying meter in an optomechanical cavity with mechanical mirror in middle configuration can enhance the sensitivity beyond the standard quantum limit by a factor of e-reff, where reff = r + ln(4Δ/ζ)/2, for 0 < ζ/Δ < 1, with ζ as the optomechanical cavity decay rate and Δ as the detuning between cavity eigenfrequency and driving field. The technique described in this work is restricted to frequencies much smaller than the resonance frequency of the mechanical mirror. We further studied the sensitivity as a function of temperature, mechanical mirror reflectivity, and input laser power.

On-Chip Microwave Frequency Combs in a Superconducting Nanoelectromechanical Device.

Nanomechanical resonances coupled to microwave cavities can be excited, measured, and controlled simultaneously using electromechanical back-action phenomena. Examples of these effects include sideband cooling and amplification, which are commonly described through linear equations of motion governed by an effective optomechanical Hamiltonian. However, this linear approximation is invalid when the pump-induced cavity microwave field is large enough to trigger optomechanical nonlinearities, resulting in phenomena like frequency combs. Here, we employ a niobium-based superconducting electromechanical device to explore the generation of microwave frequency combs. We observe the formation of combs around a microwave resonant frequency (3.78 GHz) with 8-MHz frequency spacing, equal to the mechanical resonant frequency. We investigate their dynamics for different optomechanical parameters, including detuning, pump powers, and cavity decay rates. Our experimental results show excellent agreement with numerical modeling. These electromechanical frequency combs can be beneficial in nanomechanical sensing applications that require precise electrical tracking of mechanical resonant frequencies.

Squeezing Light via Levitated Cavity Optomechanics

Squeezing light is a critical resource in both fundamental physics and precision measurement. Squeezing light has been generated through optical-parametric amplification inside an optical resonator. However, preparing the squeezing light in an optomechanical system is still a challenge for the thermal noise inevitably coupled to the system. We consider an optically levitated nano-particle in a bichromatic cavity, in which two cavity modes could be excited by the scattering photons of the dual tweezers, respectively. Based on the coherent scattering mechanism, the ultra-strong coupling between the cavity field and the torsional motion of nano-particle could be achieved for the current experimental conditions. With the back-action of the optically levitated nano-particle, the broad single-mode squeezing light can be realized in the bad cavity regime. Even at room temperature, the single-mode light can be squeezed for more than 17 dB, which is far beyond the 3 dB limit. The two-mode squeezing light can also be generated, if the optical tweezers contain two frequencies, one is on the red sideband of the cavity mode, the other is on the blue sideband. The two-mode squeezing can be maximized near the boundary of the system stable regime and is sensitive to both the cavity decay rate and the power of the optical tweezers.

Optomechanically induced grating

We suggest a flexible control of the diffraction grating by considering an optomechanical cavity system. The cavity is driven by an external control standing wave and realizes the characteristics of the diffraction grating when the light beam interacts with the cavity, a phenomenon which we name optomechanically induced grating (OMIG). A standing wave consists of nodes and antinodes that lead to gratings or slits in the cavity system. The reflected probe field from a moving mirror is diffracted through a standing wave and comes out through a partially reflected mirror. Effective control of the diffraction grating is achieved with the manipulation of the optomechanical strength g mc ( the so-called mirror-light interaction strength). Fascinatingly, the first, second, and third-order diffraction gratings can be easily achieved via the mirror-light interaction strength g mc . The diffraction grating is found to be influenced by the cavity decay rate. For small values of the decay rate, the diffraction grating becomes maximum and vice versa. The results of our model can bring potential applications in optomechanical systems.

Controllable four-wave mixing in an atom–optical cavity coupling system with a second-order nonlinear crystal

The four-wave mixing (FWM) effect has been systematically studied in an atom–optical cavity coupling system with a second-order nonlinear crystal (SOC), which is formed by coupling an optical cavity with a two-level atom and a SOC. In this research, it is found that the FWM effect largely depends on the SOC, because the SOC can promote a two-photon absorption process. Therefore, a tunable FWM signal can be obtained in this coupling system by controlling the SOC. Moreover, the results also show that the cavity decay rate plays an important role in controlling the FWM signal. By optimizing the cavity decay rate and the SOC, a strong FWM signal can be generated. In addition, by adjusting the cavity–pump detuning, conversion between a single-peak FWM signal and two-peak FWM signal can be easily realized.

Improving few-photon optomechanical effects with coherent feedback.

Few-photon effects such as photon blockade and tunneling have potential applications in modern quantum technology. To enhance the few-photon effects in an optomechanical system, we introduce a coherent feedback loop to cavity mode theoretically. By studying the second-order correlation function, we show that the photon blockade effect can be improved with feedback. Under appropriate parameters, the photon blockade effect exists even when cavity decay rate is larger than the single-photon optomechanical coupling coefficient, which may reduce the difficulty of realizing single-photon source in experiments. Through further study of the third-order correlation function, we show that the tunneling effect can also be enhanced by feedback. In addition, we discuss the application of feedback on Schrödinger-cat state generation in an optomechanical system. The result shows that the fidelity of cat state generation can be improved in the presence of feedback loop.

Two-color, intracavity pump-probe, cavity ringdown spectroscopy.

We report a proof-of-principle demonstration of intracavity pump-probe, cavity ringdown (CRD) detection in a three-mirror, traveling-wave cavity. With cavity-enhanced pump power and probe absorption path length, the technique is a generally applicable, high-sensitivity, high-selectivity detection method. In our experiments, the pump radiation is switched off during every other probe ringdown, which allows uncorrelated measurements of analyte and background cavity decay rates. The net, two-color signal from the difference between the pump-on and pump-off decay rates is immune to empty-CRD drifts and spectral overlaps from non-target molecular transitions. The immunity to the ringdown drifts allows longer signal-averaging and, thus, higher detection sensitivity. The ability to compensate for the background absorption enhances the detection selectivity in spectrally congested regions. Our technique is well-suited for trace-detection in the mid-IR region, where pump-probe schemes based on strong rovibrational transitions can be applied. In this work, two-color CRD detection is implemented on a ladder-type, three-level system based on the N2O, ν3 = 1 ← 0, P(19) (pump) and ν3 = 2 ← 1, R(18) (probe), rovibrational transitions. By frequency-locking two-quantum cascade lasers to the p-polarization (pump, Finesse = 5280) and s-polarization (probe, Finesse = 67700) cavity modes, we achieve high intracavity pump power (36W) and high probe ringdown rates (>2 kHz). The observed two-color spectra are simulated by a density-matrix, three-level system model that is solved under the constraints of the cavity resonance conditions. In addition to its background compensation capability, experimental flexibility in the selection of pump-probe schemes and signal insensitivity to intracavity laser power are further features that enhance the utility of our technique for mid-IR trace-detection.

Ideal optomechanically induced transparency generation in a cavity optoelectromechanical system* *Project supported by the Natural Science Foundation of Guangxi Province, China (Grant Nos. 2018GXNSFBA281003, 2019GXNSFAA245034, and AD19245180) and Science Fund of Tonghua Normal University (Grant No. 202017ND).

The ideal optomechanically induced transparency effects of an output probe field are investigated in a cavity optoelectromechanical system, which is composed of an optical cavity, a charged mechanical resonator, and a charged object. Although the charged mechanical resonator damping rate is nonzero, the ideal optomechanically induced transparency can still appear due to the non-rotating wave approximation effect in the system. The location of optomechanically induced transparency dip can be controlled via the Coulomb coupling strength. In addition, we find that both the transparency window width and the maximum dispersion curve slope are closely related to the optical cavity decay rate.

Photonic chip-based resonant supercontinuum via pulse-driven Kerr microresonator solitons

Supercontinuum generation and soliton microcomb formation both represent key techniques for the formation of coherent, ultrabroad optical frequency combs, enabling the RF-to-optical link. Coherent supercontinuum generation typically relies on ultrashort pulses with kilowatt peak power as a source, and so are often restricted to repetition rates less than 1 GHz. Soliton microcombs, conversely, have an optical conversion efficiency that is best at ultrahigh repetition rates such as 1 THz. Neither technique easily approaches the microwave domain, i.e., 10 s of GHz, while maintaining an ultrawide spectrum. Here, we bridge the efficiency gap between the two approaches in the form of resonant supercontinuum generation by driving a dispersion-engineered photonic-chip-based microresonator with picosecond pulses of the order of 1-W peak power. We generate a smooth 2200-line soliton-based comb at an electronically detectable 28 GHz repetition rate. Importantly, we observe that solitons exist in a weakly bound state with the input pulse where frequency noise transfer from the input pulses is suppressed even for offset frequencies 100 times lower than the linear cavity decay rate. This transfer can be reduced even further by driving the cavity asynchronously, ensuring the frequency comb stays coherent even for optical lines very far from the pump center.

Optomechanically induced ultraslow and ultrafast light

Slow and fast light is an important and fascinating phenomenon in quantum optics. Here, we theoretically study how to achieve the ultraslow and ultrafast light in a passive-active optomechanical system, based on the ideal optomechanically induced transparency (OMIT). Under the conditions of the ideal OMIT, an abnormal (inverted) transparency window will emerge accompanied with a very steep dispersion, resulting that the ultraslow light can be easily achieved at the transparency window by adjusting the dissipation rates of the two cavities, even with usual mechanical linewidth (such as Hz linewidth). Particularly, as the decay rate of the passive cavity tends to the gain rate of the active cavity, the ideal stopped light can be achieved. Similarly, the ultrafast light can be achieved at transparency window by tuning the coupling strength and the decay rates in the system.

Controllable four-wave mixing based on quantum dot-cavity coupling system

We theoretically study the four-wave mixing (FWM) response in a quantum dot-cavity coupling system, where a two-level quantum dot (QD) is placed in an optical cavity while the cavity mode is coupled to the nanomechanical resonator via radiation pressure. The influences of the QD-cavity coupling strength, the Rabi coupling strength of the QD, and the power of the pump light on the FWM intensity are mainly considered. The numerical results show that the FWM intensity in this hybrid system can be significantly enhanced by increasing the QD-cavity coupling strength. In addition, the FWM intensity can be effectively modulated by the Rabi coupling strength and the pump power. Furthermore, the effects of the cavity decay rate and the cavity-pump detuning on the FWM signal are also explored. The obtained results may have potential applications in the fields of quantum optics and quantum information science.