Squeezing Of Noise Research Articles

The “Squeeze Laser”

The level of quantum noise in measurements is bounded from below by the Heisenberg uncertainty principle, but it can be unequally distributed between two non-commuting observables — it can be “squeezed”. Since 2019, all gravitational-wave observatories have been using squeezed light for increasing the astronomical reach. Squeezed laser light is efficiently produced by degenerate parametric down-conversion in a nonlinear crystal located inside an optical resonator. A spontaneously generated initial pair of indistinguishable photons is amplified to a squeezed vacuum state. Overlapped with bright coherent light, the photo electric measurement shows a sub-Poissonian photon statistics. Squeezed states have ample applications in nonlocal quantum sensing, device-independent quantum key distribution, and quantum computing. Here, we present our continuous-wave 1550 nm ‘squeeze laser’ with a footprint of 80 cm × 80 cm. The well-defined output beam has an interference contrast of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\gtrsim 99\%$</tex-math></inline-formula> with an overlapped 10 mW beam being in an almost perfect TEM00 mode. The interference result shows 13 dB squeezing of the photon shot noise in balanced detection.

Observation of nonlinear spin dynamics and squeezing in a BEC using dynamic decoupling

We study the evolution of a Bose–Einstein condensate in a two-state superposition due to inter-state interactions. Using a population imbalanced dynamic decoupling scheme, we measure inter-state interactions while canceling intra-state density shifts and external noise sources. Our measurements show low statistical uncertainties for both magnetic sensitive and insensitive superpositions, indicating that we successfully decoupled our system from strong magnetic noises. We experimentally show that the Bloch sphere representing general superposition states is ‘twisted’ by inter-state interactions, as predicted in [, ] and the twist rate depends on the difference between inter-state and intra-state scattering lengths a 22 + a 11 − 2a 12. We use the non-linear spin dynamics to demonstrate squeezing of Gaussian noise, showing 2.79 ± 0.43 dB squeezing when starting with a noisy state and applying 160 echo pulses, which can be used to increase sensitivity when there are errors in state preparation. Our results allow for a better understanding of inter-atomic potentials in 87Rb. Our scheme can be used for spin-squeezing beyond the standard quantum limit and observing polaron physics close to Feshbach resonances, where interactions diverge, and strong magnetic noises are ever present.

Squeezing of intensity noise in nanolasers and nanoLEDs with extreme dielectric confinement

Low-noise light sources are important for on-chip interconnects, sensors, and quantum technology. We show that, using novel cavity designs featuring deep sub-wavelength confinement, it is possible to strongly reduce quantum fluctuations over a large bandwidth. The results could enable integrated sources with extremely low amplitude noise.

Improved squeezing of noise

Two articles in Nature Photonics demonstrate how Einstein–Podolsky–Rosen entanglement can reduce quantum noise in gravitational-wave interferometers.

High-Efficiency Measurement of an Artificial Atom Embedded in a Parametric Amplifier

A crucial limit to measurement efficiencies of superconducting circuits comes from losses involved when coupling to an external quantum amplifier. Here, we realize a device circumventing this problem by directly embedding a two-level artificial atom, comprised of a transmon qubit, within a flux-pumped Josephson parametric amplifier. Surprisingly, this configuration is able to enhance dispersive measurement without exposing the qubit to appreciable excess backaction. This is accomplished by engineering the circuit to permit high-power operation that reduces information loss to unmonitored channels associated with the amplification and squeezing of quantum noise. By mitigating the effects of off-chip losses downstream, the on-chip gain of this device produces end-to-end measurement efficiencies of up to 80 percent. Our theoretical model accurately describes the observed interplay of gain and measurement backaction, and delineates the parameter space for future improvement. The device is compatible with standard fabrication and measurement techniques, and thus provides a route for definitive investigations of fundamental quantum effects and quantum control protocols.

Revealing Hidden Quantum Correlations in an Electromechanical Measurement.

Under a strong quantum measurement, the motion of an oscillator is disturbed by the measurement backaction, as required by the Heisenberg uncertainty principle. When a mechanical oscillator is continuously monitored via an electromagnetic cavity, as in a cavity optomechanical measurement, the backaction is manifest by the shot noise of incoming photons that becomes imprinted onto the motion of the oscillator. Following the photons leaving the cavity, the correlations appear as squeezing of quantum noise in the emitted field. Here we observe such "ponderomotive" squeezing in the microwave domain using an electromechanical device made out of a superconducting resonator and a drumhead mechanical oscillator. Under a strong measurement, the emitted field develops complex-valued quantum correlations, which in general are not completely accessible by standard homodyne measurements. We recover these hidden correlations, using a phase-sensitive measurement scheme employing two local oscillators. The utilization of hidden correlations presents a step forward in the detection of weak forces, as it allows us to fully utilize the quantum noise reduction under the conditions of strong force sensitivity.

Dispersive response of atoms trapped near the surface of an optical nanofiber with applications to quantum nondemolition measurement and spin squeezing

We study the strong coupling between photons and atoms that can be achieved in an optical nanofiber geometry when the interaction is dispersive. While the Purcell enhancement factor for spontaneous emission into the guided mode does not reach the strong-coupling regime for individual atoms, one can obtain high cooperativity for ensembles of a few thousand atoms due to the tight confinement of the guided modes and constructive interference over the entire chain of trapped atoms. We calculate the dyadic Green's function, which determines the scattering of light by atoms in the presence of the fiber, and thus the phase shift and polarization rotation induced on the guided light by the trapped atoms. The Green's function is related to a full Heisenberg-Langevin treatment of the dispersive response of the quantized field to tensor polarizable atoms. We apply our formalism to quantum nondemolition (QND) measurement of the atoms via polarimetry. We study shot-noise-limited detection of atom number for atoms in a completely mixed spin state and the squeezing of projection noise for atoms in clock states. Compared with squeezing of atomic ensembles in free space, we capitalize on unique features that arise in the nanofiber geometry including anisotropy of both the intensity and polarization of the guided modes. We use a first principles stochastic master equation to model the squeezing as function of time in the presence of decoherence due to optical pumping. We find a peak metrological squeezing of ~5 dB is achievable with current technology for ~2500 atoms trapped 180 nm from the surface of a nanofiber with radius a=225 nm.

Squeezing of Quantum Noise of Motion in a Micromechanical Resonator.

A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations that are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude 1.1±0.4 dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object.

Nonclassicality in Raman scattering: Quantum entanglement, squeezing of vacuum fluctuations, sub-shot noise and joint photon–phonon number and integrated-intensity distributions

A completely quantum description of Raman process is used to investigate the nonclassical properties of the modes in the stimulated, spontaneous and partially spontaneous Raman process. Both coherent scattering (where all the initial modes are coherent) and chaotic scattering (where initial phonon mode is chaotic and all the other modes are coherent) are studied. Nonclassical character of Raman process is observed by means of intermodal entanglement, single mode and intermodal squeezing of vacuum fluctuations, sub-shot noise and wave variances. Joint photon-phonon number and integrated-intensity distributions are then used to illustrate the observed nonclassicalities. Conditional and difference number distributions are also provided to illustrate the nonclassical character. The mutual relation between the obtained nonclassicalities and their variations dependent on phases, rescalled time and ratio of coupling constants are also reported.

Highly Nonlinear and Dispersion-Flattened Fiber Design for Ultrafast Phase-Sensitive Amplification

The properties of phase-sensitive amplification (PSA) in highly nonlinear fibers are studied. We present a soft glass fiber designed for high nonlinearity and broadband, low dispersion and simulate its performance as a PSA device for ultrafast bitrate signals at 640 Gb/s. The effect of the fiber design parameters on its PSA performance have been studied and the final design has been optimized using a genetic algorithm to have a high nonlinearity and low, flat dispersion. This design has subsequently been compared to other highly nonlinear fibers in order to highlight the effect of both using soft glass and the design and optimization technique. Modelled fiber performance shows squeezing of phase noise in a 5 m length of fiber with 32 dBm total power in the signal and pumps. The fiber length we have used in our model is two orders of magnitude shorter than the state of the art silica based PSA devices for comparable power levels. In addition, fabrication tolerance modelling is done to show that our fiber design is better able to manage fluctuations in the dispersion due to the high nonlinearity.

Squeezing of atomic quantum projection noise

We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we consider a dual probe scheme which benefits from a cancelation of classical common mode noise sources such that quantum fluctuations from light and atoms are the main contributions to the detected signal.

Broadband squeezing of quantum noise in a Michelson interferometer with Twin-Signal-Recycling

Twin-Signal-Recycling (TSR) builds on the resonance doublet of two optically coupled cavities and efficiently enhances the sensitivity of an interferometer at a dedicated signal frequency. We report on what we believe to be the first experimental realization of a TSR Michelson interferometer and also its broadband enhancement by squeezed light injection. The complete setup was stably locked, and a broadband quantum noise reduction of the interferometers shot noise by a factor of up to 4 dB was demonstrated. The system was characterized by measuring its quantum noise spectra for several tunings of the TSR cavities. We found good agreement between the experimental results and numerical simulations.

Amplification and squeezing of quantum noise with a tunable Josephson metamaterial

An array of 488 Josephson junctions that amplifies and squeezes noise beyond conventional quantum limits should prove useful in the study and development of superconducting qubits and other quantum devices.

Observation of Squeezed Light with 10-dB Quantum-Noise Reduction

Squeezing of light's quantum noise requires temporal rearranging of photons. This again corresponds to creation of quantum correlations between individual photons. Squeezed light is a nonclassical manifestation of light with great potential in high-precision quantum measurements, for example, in the detection of gravitational waves [C. M. Caves, Phys. Rev. D 23, 1693 (1981)10.1103/PhysRevD.23.1693]. Equally promising applications have been proposed in quantum communication [H. P. Yuen and J. H. Shapiro, IEEE Trans. Inf. Theory 24, 657 (1978)10.1109/TIT.1978.1055958]. However, after 20 years of intensive research doubts arose whether strong squeezing can ever be realized as required for eminent applications. Here we show experimentally that strong squeezing of light's quantum noise is possible. We reached a benchmark squeezing factor of 10 in power (10 dB). Thorough analysis reveals that even higher squeezing factors will be feasible in our setup.

Quantum Monte Carlo study of ring-shaped polariton parametric luminescence in a semiconductor microcavity

We present a quantum Monte Carlo study of the quantum correlations in the parametric luminescence from semiconductor microcavities in the strong exciton-photon coupling regime. As already demonstrated in recent experiments, a ring-shaped emission is obtained by applying two identical pump beams with opposite in-plane wavevectors, providing symmetrical signal and idler beams with opposite in-plane wavevectors on the ring. We study the squeezing of the signal-idler difference noise across the parametric instability threshold, accounting for the radiative and non-radiative losses, multiple scattering and static disorder. We compare the results of the complete multimode Monte Carlo simulations with a simplified linearized quantum Langevin analytical model.

The hyperbolic, the arithmetic and the quantum phase

We develop a new approach of the quantum phase in an Hilbert space of finite dimension which is based on the relation between the physical concept of phase locking and mathematical concepts such as cyclotomy and the Ramanujan sums. As a result, phase variability looks quite similar to its classical counterpart, having peaks at dimensions equal to a power of a prime number. Squeezing of the phase noise is allowed for specific quantum states. The concept of phase entanglement for Kloosterman pairs of phase-locked states is introduced.

Generation and manipulation of squeezed states of light in optical networks for quantum communication and computation

We analyze a fiber-optic component which could find multiple uses in novel information-processing systems utilizing squeezed states of light. Our approach is based on the phenomenon of photon-number squeezing of soliton noise after the soliton has propagated through a nonlinear optical fiber. Applications of this component in optical networks for quantum computation and quantum cryptography are discussed.

PHOTON NOISE SQUEEZING AND ITS PHYSICAL MECHANISM OF A DRIVEN V-TYPE THREE-LEVEL LASER

Photon noise squeezing and its physical mechanism of a driven V-type three-level laser are investigated via Scully-Lamb theory.It is shown that intracavity squeezing of 10% and extracavity squeezing of 20% can be achieved.Even if the amount of squeezing in V system is smaller than that in Λ system (intracavity squeezing and extracavity squeezing of up to 50%),both systems have the same mechanism responsible for the squeezing of photon noise.

THE OPERATION IN THE STEADY STATE AND SQUEEZING OF QUANTUM NOISE IN TWO-MODE TWO-PHOTON CORRELATED-SPONTANEOUS-EMISSION LASERS

Operation in the steady state and squeezing of quantum noise in two-mode two-photon correlated-spontaneous-emission lasers(CEL) are studied via nonliner quantum theory.It is shown that the two-mode two-photon CEL exhibits lasing without inversion and two-mode hysteresis even without triggering.The features of squeezing of quantum noise in the relative amplitude and the average phase are given.

Optical displacement sensor with frequency-selective squeezing of the vacuum noise

Electromechanical analogies are used to derive expressions for the electromechanical Z parameters and for the energy spectra of Langevin sources of noise in an lf equivalent of an optical displacement sensor with frequency-selective squeezing of the vacuum noise. The minimum noise temperature of the sensor is estimated. The use of squeezed vacuum fluctuations can improve the noise matching of the sensor and help to achieve the minimum noise temperature even for nonoptimal parameters of the system.