Spectrum Of Squeezing Research Articles

Optical response properties of a hybrid optomechanical system with quantum dot molecules assisted by second-order optomechanical coupling

We theoretically investigated the optical response properties of the optical field in three-level quantum dot molecules assisted optomechanical system consisting of the mechanical resonator. We show that various system parameters like second-order optomechanical coupling can control these nonlinear effects. In this work, we study how the system parameters affect the normal mode splitting of the movable mirror and output field. Further, we show that the second-order optomechanical coupling plays an important role in creating optomechanical entanglement as well as producing a strong squeezing spectrum of the optical field.

Entanglement and output squeezing in a distant nano-electro-optomechanical system generated by optical parametric amplifiers

We investigate the entanglement phenomena assisted by a distant nono-electro-optomechanical system with two optical parametric amplifiers. The system consists of two optomechanical cavities coupling to two charged mechanical resonators via Coulomb interaction. Under suitable conditions, the movable mirrors and the two distant cavity fields can exhibit entanglement. The entanglement is strongly manipulated by the parametric gain and the Coulomb coupling. Furthermore, because of the introduction of the charged mechanical oscillators, the entanglement between the two cavity modes and between the movable mirrors displays a splitting phenomenon. We also study the squeezing spectrum of the cavity fields. The results reveal that the output squeezing of the two cavity fields is affected by the frequency of the mirror oscillation and the parametric gain.

Nonlinear quantum behavior of ultrashort-pulse optical parametric oscillators

The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are investigated theoretically in the nonlinear regime near and above threshold. Viewing the pulsed OPO as a multimode open quantum system, we rigorously derive a general input-output model that features nonlinear coupling among many cavity (i.e., system) signal modes and a broadband single-pass (i.e., reservoir) pump field. Under appropriate assumptions, our model produces a Lindblad master equation with multimode nonlinear Lindblad operators describing two-photon dissipation and a multimode four-wave-mixing Hamiltonian describing a broadband, dispersive optical cascade, which we show is required to preserve causality. To simplify the multimode complexity of the model, we employ a supermode decomposition to perform numerical simulations in the regime where the pulsed supermodes experience strong single-photon nonlinearity. We find that the quantum nonlinear dynamics induces pump depletion as well as corrections to the below-threshold squeezing spectrum predicted by linearized models. We also observe the formation of non-Gaussian states with Wigner-function negativity and show that the multimode interactions with the pump, both dissipative and dispersive, can act as effective decoherence channels. Finally, we briefly discuss some experimental considerations for potentially observing such quantum nonlinear phenomena with ultrashort-pulse OPOs on nonlinear nanophotonic platforms.

Unraveling Two-Photon Entanglement via the Squeezing Spectrum of Light Traveling through Nanofiber-Coupled Atoms.

We observe that a weak guided light field transmitted through an ensemble of atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the measured squeezing spectrum we gain direct access to the phase and amplitude of the energy-time entangled part of the two-photon wave function which arises from the strongly correlated transport of photons through the ensemble. For small atomic ensembles we observe a spectrum close to the line shape of the atomic transition, while sidebands are observed for sufficiently large ensembles, in agreement with our theoretical predictions. Furthermore, we vary the detuning of the probe light with respect to the atomic resonance and infer the phase of the entangled two-photon wave function. From the amplitude and the phase of the spectrum, we reconstruct the real and imaginary part of the time-domain wave function. Our characterization of the entangled two-photon component constitutes a diagnostic tool for quantum optics devices.

Quantum optomechanical system in a Mach-Zehnder interferometer

We consider an oscillating micromirror replacing one of the two fixed mirrors of a Mach-Zehnder interferometer. In this ideal optical set-up the quantum oscillator is subjected to the radiation pressure interaction of travelling light waves, no cavity is involved. This configuration shows that squeezed light can be generated by pure scattering on a quantum system, without involving a cavity. The squeezing can be detected at the output ports of the interferometer either by direct detection or by measuring the spectrum of the difference current. We use the Hudson-Parthasarathy equation to model the global evolution. It can describe the scattering of photons and the resulting radiation pressure interaction on the quantum oscillator. It allows to consider also the interaction with a thermal bath. In this way we have a unitary dynamics giving the evolution of oscillator and fields. The Bose fields of quantum stochastic calculus and the related generalized Weyl operators allow to describe the whole optical circuit. By working in the Heisenberg picture, the quantum Langevin equations for position and momentum and the output fields arise, which are used to describe the monitoring in continuous time of the light at the output ports. In the case of strong laser and weak radiation pressure interaction highly non-classical light is produced, and this can be revealed either by direct detection (a negative Mandel Q-parameter is found), either by the intensity spectrum of the difference current of two photodetector; in the second case a nearly complete cancellation of the shot noise can be reached. In this last case it appears that the Mach-Zehnder configuration together with the detection of the difference current corresponds to an homodyne detection scheme, so that we can say that the apparatus is measuring the spectrum of squeezing.

Tunable ponderomotive squeezing in an optomechanical system with two coupled resonators* *Project supported by the Doctoral Program of Guangdong Natural Science Foundation,China (Grant No. 2018A030310109), the Doctoral Project of Guangdong Medical University (Grant No. B2017019), and the Project of Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education of China (Grant No. QSQC1808).

We investigate properties of the ponderomotive squeezing in an optomechanical system with two coupled resonators, where the tunable two-mode squeezing spectrum can be observed from the output field. It is realized that the squeezing orientation can be controlled by the detuning between the left cavity and pump laser. Especially, both cavity decay and environment temperature play a positive role in generating better pondermotive squeezing light. Strong squeezing spectra with a wide squeezing frequency range can be obtained by appropriate choice of parameters present in our optomechanical system.

Bloch-Messiah decomposition and Magnus expansion for parametric down-conversion with monochromatic pump: role of the gain

We consider the effect of different orders of Magnus expansion for the field transformation in type-I parametric down-conversion with a monochromatic pump. The exact solution, existing in this case, allows us to analyze the convergence of the Magnus expansion for the spectrum of squeezing and the angle of squeezing. We demonstrate how the convergence of the Magnus series depends on the parametric gain for various values of the phase mismatch. For each phase-mismatch angle we find the gain, which is the exact upper bound for the convergence of the Magnus series.

Output field squeezing in a weakly-driven dissipative quantum Rabi model

Abstract We present a generalized method to address the squeezing spectrum of the output field for a weakly-driven, dissipative quantum Rabi model and calculate it for a range of coupling strengths covering strong, ultra-strong and deep-strong coupling regimes. The need for a generalization arises because of the periodic time dependence of the correlation functions due to counter rotating terms in the quantum Rabi model. We here adopt time-averaging over such correlation functions to obtain the squeezing spectrum, which may also be relevant to experimental situations. We compare the calculated squeezing spectra with those of the driven dissipative Jaynes–Cummings model to illustrate the departure from the latter as the interaction strength increases. Our calculation shows that the overall squeezing increases with the interaction strength after optimization over the system-bath coupling strength and the driving field strength.

Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit

A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.

Integrated source of broadband quadrature squeezed light.

An integrated silicon nitride resonator is proposed as an ultra-compact source of bright single-mode quadrature squeezed light at 850 nm. Optical properties of the device are investigated and tailored through numerical simulations, with particular attention paid to loss associated with interfacing the device. An asymmetric double layer stack waveguide geometry with inverse vertical tapers is proposed for efficient and robust fibre-chip coupling, yielding a simulated total loss of -0.75 dB/facet. We assess the feasibility of the device through a full quantum noise analysis and derive the output squeezing spectrum for intra-cavity pump self-phase modulation. Subject to standard material loss and detection efficiencies, we find that the device holds promises for generating substantial quantum noise squeezing over a bandwidth exceeding 1 GHz. In the low-propagation loss regime, approximately -6 dB squeezing is predicted for a pump power of only 75 mW.

Towards single-cycle squeezing in chirped quasi-phase-matched optical parametric down-conversion

We propose a method for generation of single-cycle squeezed light by parametric down-conversion in a chirped quasi-phase-matched nonlinear crystal. We find an exact quantum solution for this process valid for an arbitrary parametric gain (under an assumption of nondepleted pump), and discover an ultrabroadband squeezing in the down-converted light with a flat squeezing spectrum comprising the full optical octave. We describe a scheme for observation of this kind of squeezing using second-harmonic generation as an ultrafast correlator.

Squeezed light in an optical parametric oscillator network with coherent feedback quantum control

We present squeezing and anti-squeezing spectra of the output from a degenerate optical parametric oscillator (OPO) network arranged in different coherent quantum feedback configurations. One OPO serves as a quantum plant, the other as a quantum controller. The addition of coherent feedback enables shaping of the output squeezing spectrum of the plant, and is found to be capable of pushing the frequency of maximum squeezing away from the optical driving frequency and broadening the spectrum over a wider frequency band. The experimental results are in excellent agreement with the developed theory, and illustrate the use of coherent quantum feedback to engineer the quantum-optical properties of the plant OPO output.

Phase-dependent squeezing and entanglement in a cavity QED

The output squeezed spectrum of the output two modes from a cavity QED system which is embedded by a four-level atom driven by two classical fields are calculated. The effects of the cavity decay rates, relative phase between two classical fields, and effective coupling constants between the atom and the cavity on the entanglement and squeezing of the two cavity modes are investigated. It is shown that the depth of the squeezing or entanglement spectrum is insensitive to the cavity decay rates while its width is dependent on the cavity decay rates and the coupling constants. In particular, the squeezing or entanglement spectrum including their maximal values and widths is remarkably affected by the relative phase between the classical fields. It is found that the output spectrum varies with the relative phase in a cosine-like behavior with a period of 2π. The results can indicate how to suitably adjust the relative phase for acquiring maximal squeezing or perfect entanglement for the two cavity fields. This will be useful in quantum communication and computation.

Quantum optomechanics with a high-frequency dilational mode in thin dielectric membranes

The interaction between a high-frequency dilational mode of a thin dielectric film and an optical cavity field is studied theoretically in the membrane-in-the-middle setup. A derivation from first principles leads to a multi-mode optomechanical Hamiltonian where multiple cavity modes are coupled by the thickness variation of the membrane. For membrane thicknesses of the order of 1 μm, the frequency of this dilational mode is in the GHz range. This can be matched to the free spectral range of the optical cavity, such that the mechanical oscillator will resonantly couple cavity modes at different frequencies. Furthermore, such a large mechanical frequency also means that the quantum ground state of motion can be reached with conventional refrigeration techniques. Estimation of the coupling strength with realistic parameters suggests that optomechanical effects can be observable with this dilational mode. It is shown how this system can be used as a quantum limited optical amplifier. The dilational motion can also lead to quantum correlations between cavity modes at different frequencies, which is quantified with an experimentally accessible two-mode squeezing spectrum. Finally, an explicit signature of radiation pressure shot noise in this system is identified.

Squeezing and entanglement of a two-mode field in a four-level tripod atomic system

The interaction of a collection of N four-level tripod configuration atoms with two orthogonally polarized probe fields is investigated. Under the condition of electromagnetically induced transparency (EIT), we calculate the squeezing and entanglement spectra of the output probe fields. By analyzing the output spectrum, we find that the squeezing and entanglement of the probe fields can be well-preserved after passing through the optically thick medium. Additionally, the effects of the ground state dephasing rates of the atoms on the entanglement and squeezing of the output two-mode squeezed fields are investigated. It is shown that the dephasing rates will degrade the entanglement and squeezing, and these quantum properties can be lost when the dephasing rates increase up to a certain value. This will be useful in the quantum computation and quantum communication.

Phase sensitive two-mode squeezing and photon correlations from exciton superfluid in semiconductor electron-hole bilayer systems

There have been experimental and theoretical studies on Photoluminescence (PL) from possible exciton superfluid in semiconductor electron-hole bilayer systems. However, the PL contains no phase information and no photon correlations, so it can only lead to suggestive evidences. It is important to identify smoking gun experiments which can lead to convincing evidences. Here we study two mode phase sensitive squeezing spectrum and also two photon correlation functions. We find the emitted photons along all tilted directions are always in a two mode squeezed state between $ \vec{k} $ and $ - \vec{k} $. There are always two photon bunching, the photon statistics is super-Poissonian. Observing these unique features by possible future phase sensitive homodyne experiment and HanburyBrown-Twiss type of experiment could lead to conclusive evidences of exciton superfluid in these systems.

Giant Kerr Nonlinearities in Circuit Quantum Electrodynamics

The very small size of optical nonlinearities places strict restrictions on the types of novel physics one can explore. This work describes how a single artificial multilevel Cooper pair box molecule, interacting with a superconducting microwave coplanar resonator, when suitably driven, can generate extremely large optical nonlinearities at microwave frequencies, with no associated absorption. We describe how the giant self-Kerr effect can be detected by measuring the second-order correlation function and quadrature squeezing spectrum.

Output entanglement and squeezing of two-mode fields generated by a single atom

A single four-level atom interacting with two-mode cavities is investigated. Under large detuning condition, we obtain the effective Hamiltonian which is unitary squeezing operator of two-mode fields. Employing the input–output theory, we find that the entanglement and squeezing of the output fields can be achieved. By analyzing the squeezing spectrum, we show that asymmetric detuning and asymmetric atomic initial state split the squeezing spectrum from one valley into two minimum values, and appropriate leakage of the cavity is needed for obtaining output entangled fields.

Squeezed single-atom laser in a photonic crystal

We study nonclassical and spectral properties of a strongly driven single-atom laser engineered within a photonic crystal that facilitates a frequency-dependent reservoir. In these studies, we apply a dressed atom model approach to derive the master equation of the system and study the properties of the dressed laser under the frequency-dependent transition rates. By going beyond the secular approximation in the dressed-atom cavity-field interaction, we find that if, in addition, the nonsecular terms are included into the dynamics of the system, then nonlinear processes can occur that lead to interesting aspects of cavity field behavior. We calculate variances of the quadrature phase amplitudes and the incoherent part of the spectrum of the cavity field and show that they differ qualitatively from those observed under the secular approximation. In particular, it is found that the nonlinear processes lead to squeezing of the fluctuations of the cavity field below the quantum shot noise limit. The squeezing depends on the relative population of the dressed states of the system and is found only if there is no population inversion between the dressed states. Furthermore, we find a linewidth narrowing below the quantum limit in the spectrum of the cavity field that is achieved only when the secular approximation is not made. An interpretation of the linewidth narrowing is provided in terms of two phase-dependent noise (squeezing) spectra that make up the incoherent spectrum. We establish that the linewidth narrowing is due to squeezing of the fluctuations in one quadrature phase components of the cavity field.

Nonlinear optics with two trapped atoms

We show theoretically that two atomic dipoles in a resonator constitute a nonlinear medium, whose properties can be controlled through the relative position of the atoms inside the cavity and the detuning and intensity of the driving laser. We identify the parameter regime where the system operates as a parametric amplifier, based on the cascade emission of the collective dipole of the atoms, and determine the corresponding spectrum of squeezing of the field at the cavity output. This dynamics might be observed as a result of self-organization of laser-cooled atoms in resonators.