Quantum Noise Properties Research Articles

Noiseless photonic non-reciprocity via optically-induced magnetization

The realization of optical non-reciprocity is crucial for many applications, and also of fundamental importance for manipulating and protecting the photons with desired time-reversal symmetry. Recently, various new mechanisms of magnetic-free non-reciprocity have been proposed and implemented, avoiding the limitation of the strong magnetic field imposed by the Faraday effect. However, due to the difficulties in separating the signal photons from the drive laser and the noise photons induced by the drive laser, these devices exhibit limited isolation performances and their quantum noise properties are rarely studied. Here, we demonstrate an approach of magnetic-free non-reciprocity by optically-induced magnetization in an atom ensemble. Excellent isolation (highest isolation ratio is 51.{5}_{-2.5}^{+6.5} {rm{dB}}) is observed over a power dynamic range of 7 orders of magnitude, with the noiseless property verified by quantum statistics measurements. The approach is applicable to other atoms and atom-like emitters, paving the way for future studies of integrated photonic non-reciprocal devices.

Quantum properties of light propagating in a coherent-population-oscillation storage medium

We study the propagation and storage of a quantum field using ultranarrow coherent population oscillations (CPOs) in a $\mathrm{\ensuremath{\Lambda}}$-type atomic medium. The predictions for classical fields are checked experimentally in a vapor at room temperature. We derive the evolution of its squeezing spectrum in the presence of a large classical pump field which enables CPOs to exist. We show that the spontaneous emission of the residual population pumped into the excited state progressively destroys the quantum noise properties of the quantum field along propagation. The output quantum field therefore tends to be a coherent state, discarding the possibility to store quantum states of light with CPO.

Effects of Raman scattering and attenuation in silica fiber-based parametric frequency conversion

Four-wave mixing in the form of Bragg scattering (BS) has been predicted to enable quantum noise-less frequency conversion by analytic quantum approaches. Using a semi-classical description of quantum noise that accounts for loss and stimulated and spontaneous Raman scattering, which are not currently described in existing quantum approaches, we quantify the impacts of these effects on the conversion efficiency and on the quantum noise properties of BS in terms of an induced noise figure (NF). We give an approximate closed-form expression for the BS conversion efficiency that includes loss and stimulated Raman scattering, and we derive explicit expressions for the Raman-induced NF from the semi-classical approach used here. We find that Raman scattering induces a NF in the BS process that is comparable to the 3-dB NF associated with linear amplifiers.

Measurements of nanoresonator-qubit interactions in a hybrid quantum electromechanical system

Experiments to probe the basic quantum properties of motional degrees of freedom of mechanical systems have developed rapidly over the last decade. One promising approach is to use hybrid electromechanical systems incorporating superconducting qubits and microwave circuitry. However, a critical challenge facing the development of these systems is to achieve strong coupling between mechanics and qubits while simultaneously reducing coupling of both the qubit and mechanical mode to the environment. Here we report measurements of a qubit-coupled mechanical resonator system consisting of an ultra-high-frequency nanoresonator and a long coherence-time superconducting transmon qubit, embedded in a superconducting coplanar waveguide cavity. It is demonstrated that the nanoresonator and transmon have commensurate energies and transmon coherence times are one order of magnitude larger than for all previously reported qubit-coupled nanoresonators. Moreover, we show that numerical simulations of this new hybrid quantum system are in good agreement with spectroscopic measurements and suggest that the nanoresonator in our device resides at low thermal occupation number, near its ground state, acting as a dissipative bath seen by the qubit. We also outline how this system could soon be developed as a platform for implementing more advanced experiments with direct relevance to quantum information processing and quantum thermodynamics, including the study of nanoresonator quantum noise properties, reservoir engineering, and nanomechanical quantum state generation and detection.

Quantum and classical separability of spin-orbit laser modes

In this work we investigate the quantum noise properties of polarization vortices in connection with an intensity based Clauser-Horne-Shimony-Holt inequality for their spin-orbit separability. We evaluate the inequality for different input quantum states and the corresponding intensity fluctuations. The roles played by coherence and photon number squeezing provide a suitable framework for characterizing pure state spin-orbit entanglement. Structural inseparability of the spin-orbit mode requires coherence, an issue concerning either classical or quantum descriptions. In both cases, it can be witnessed by violation of this intensity based CHSH inequality. However, in the quantum domain, entanglement requires both coherence and reduced photon number fluctuations.

Observation and Interpretation of Motional Sideband Asymmetry in a Quantum Electromechanical Device

Quantum electro-mechanical systems offer a unique opportunity to probe quantum noise properties in macroscopic devices, properties which ultimately stem from the Heisenberg Uncertainty Principle. A simple example of this is expected to occur in a microwave parametric transducer, where mechanical motion generates motional sidebands corresponding to the up and down frequency-conversion of microwave photons. Due to quantum vacuum noise, the rates of these processes are expected to be unequal. We measure this fundamental imbalance in a microwave transducer coupled to a radio-frequency mechanical mode, cooled near the ground state of motion. We also discuss the subtle origin of this imbalance: depending on the measurement scheme, the imbalance is most naturally attributed to the quantum fluctuations of either the mechanical mode or of the electromagnetic field.

Quantum noise properties of CT images with anatomical textured backgrounds across reconstruction algorithms: FBP and SAFIRE.

Quantum noise properties of CT images are generally assessed using simple geometric phantoms with uniform backgrounds. Such phantoms may be inadequate when assessing nonlinear reconstruction or postprocessing algorithms. The purpose of this study was to design anatomically informed textured phantoms and use the phantoms to assess quantum noise properties across two clinically available reconstruction algorithms, filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE). Two phantoms were designed to represent lung and soft-tissue textures. The lung phantom included intricate vessel-like structures along with embedded nodules (spherical, lobulated, and spiculated). The soft tissue phantom was designed based on a three-dimensional clustered lumpy background with included low-contrast lesions (spherical and anthropomorphic). The phantoms were built using rapid prototyping (3D printing) technology and, along with a uniform phantom of similar size, were imaged on a Siemens SOMATOM Definition Flash CT scanner and reconstructed with FBP and SAFIRE. Fifty repeated acquisitions were acquired for each background type and noise was assessed by estimating pixel-value statistics, such as standard deviation (i.e., noise magnitude), autocorrelation, and noise power spectrum. Noise stationarity was also assessed by examining the spatial distribution of noise magnitude. The noise properties were compared across background types and between the two reconstruction algorithms. In FBP and SAFIRE images, noise was globally nonstationary for all phantoms. In FBP images of all phantoms, and in SAFIRE images of the uniform phantom, noise appeared to be locally stationary (within a reasonably small region of interest). Noise was locally nonstationary in SAFIRE images of the textured phantoms with edge pixels showing higher noise magnitude compared to pixels in more homogenous regions. For pixels in uniform regions, noise magnitude was reduced by an average of 60% in SAFIRE images compared to FBP. However, for edge pixels, noise magnitude ranged from 20% higher to 40% lower in SAFIRE images compared to FBP. SAFIRE images of the lung phantom exhibited distinct regions with varying noise texture (i.e., noise autocorrelation/power spectra). Quantum noise properties observed in uniform phantoms may not be representative of those in actual patients for nonlinear reconstruction algorithms. Anatomical texture should be considered when evaluating the performance of CT systems that use such nonlinear algorithms.

Raman and loss induced quantum noise in depleted fiber optical parametric amplifiers

We present a semi-classical approach for predicting the quantum noise properties of fiber optical parametric amplifiers. The unavoidable contributors of noise, vacuum fluctuations, loss-induced noise, and spontaneous Raman scattering, are included in the analysis of both phase-insensitive and phase-sensitive amplifiers. We show that the model agrees with earlier fully quantum approaches in the linear gain regime, whereas in the saturated gain regime, in which the classical equations are valid, we predict that the amplifier increases the signal-to-noise ratio by generating an amplitude-squeezed state of light. Also, in the same process, we analyze the quantum noise properties of the pump, which is difficult using standard quantum approaches, and we discover that the pump displays complicated dynamics in both the linear and the nonlinear gain regimes.

Multimode theory of pulsed-twin-beam generation using a high-gain fiber-optical parametric amplifier

Using the Bogoliubov transformation in multi-frequency modes to describe the evolution of the non-degenerate signal and idler twin beams, we theoretically investigate the quantum noise properties of the pulse pumped high gain fiber optical parametric amplifiers (FOPA). The results show that the noise figure of the FOPA is generally greater than the 3 dB quantum limit unless the joint spectral function is factorable and the spectrum of the input signal well matches the gain spectrum in the signal band. However, the intensity difference noise of the twin beams, which weakly depends on the joint spectral function, can be significantly less than the shot-noise limit when the temporal modes of the pump and the input signal are properly matched. Moreover, to closely resemble the real experimental condition, the quantum noise of twin beams generated from a broadband FOPA is numerically studied by taking the various kinds of experimental imperfections into account. Our study is not only useful for developing a compact fiber source of twin beams, but also helpful for understanding the quantum noise limit of a pulse pumped FOPA in the fiber communication system.

Quantum noise properties of multiphoton transitions in driven nonlinear resonators

We investigate the quantum noise properties of a weakly nonlinear Duffing resonator in the deep quantum regime, where only a few quanta are excited. This regime is dominated by the appearance of coherent multiphoton resonances in the nonlinear response of the resonator to the modulation. We determine simple expressions for the photon noise spectrum and find that the multiphoton resonances also induce a multiple peak structure in that spectrum. When the corresponding multiphoton Rabi oscillations are underdamped, zero-temperature quantum fluctuations determine comparable populations of all quasienergy states which belong to a resonant multiphoton doublet. Most interestingly, the quantum fluctuations probe the multiphoton transitions by inducing several peaks in the noise spectrum of the resonator observables. In particular, the noise of the photon number contains complete information about the multiphoton states and their stationary populations via pairs of nearly symmetric peaks at opposite frequencies. Their widths are determined by the damping of the Rabi oscillations and their heights are proportional to the stationary nonequilibrium populations. A finite detuning from a multiphoton resonance generates a quasielastic noise peak at zero frequency. In addition, we relate the stationary populations of the quasienergy states with an effective quantum temperature and discuss the role of a finite temperature.

Disentanglement of three-qubit states in a noisy environment

By applying a modified conjugate gradient method in the evaluation of three-qubit residual entanglement, the disentanglement of three-qubit states in an amplitude-damping and dephasing environment is investigated numerically. It is found that the decay of tripartite entanglement is faster than bipartite entanglement in the same qubits-noise system, which indicates that multipartite entanglement is more fragile than bipartite entanglement in resisting quantum noises. Similar to the case of a two-qubit system, three-qubit entanglement subject to an open environment may also disappear abruptly (sudden death) or decrease asymptotically, which is dependent on the conditions of the initially entangled quantum state and the properties of quantum noise.

Quantum shot noise of conductors and general noise measurement methods

We review the quantum noise properties of phase coherent conductors, in particular the spectacular noise suppression associated with conductance quantization. We describe general techniques used to measure the tiny quantum shot noise current fluctuations at sub-kelvin temperature for low and high frequency.

SQUEEZING AND FIBER-OPTIC COMMUNICATIONS

We review the relations between squeezing and optical communication advances and introduce the field of distributed phase-sensitive amplification, where we expect this cross-fertilization to happen next. We consider the quantum noise properties of phase-sensitive amplifiers in lossy fiber in the case of arbitrary parametric gain distribution along the fiber length. Three most important cases of gain followed by loss, loss followed by gain, and ideally distributed gain, are discussed in detail. We show that ideally distributed phase-sensitive amplifier maximizes the signal-to-noise ratio for a fixed non-linear phase shift in the fiber span, and is promising for both classical and quantum communications.

Quantum-noise theory for terahertz hot electron bolometer mixers

In this paper, we first review general quantum mechanical limits on the sensitivity of heterodyne receivers. The main aim of the paper is to explore the quantum-noise (QN) properties of hot electron bolometric (HEB) mixers. HEB mixers have a characteristic feature not found in other mixers: based on the "hot-spot" model, the conversion loss varies along the length dimension of the bolometer, and some sections of the bolometer are essentially passive, in which little frequency conversion occurs. We analyze a quantitative distributed quantum-noise model of the HEB mixer, making use of simulated hot-spot model data, that takes into account the continuous variation of the sensitivity along the bolometer bridge. An expression for the HEB receiver noise temperature, including optical input loss, is derived. We find that the predicted double-sideband receiver noise temperature agrees well with the available measured data (up to 5.3 THz). The results of our analysis suggest that QN and classical HEB noise contribute about equally at 3 THz, while at higher terahertz frequencies QN dominates. QN thus appears to show measurable effects in existing HEB mixers and will be even more important to take into account as HEB mixers continue to be developed for higher terahertz frequencies.

Quantum-noise properties of matter-wave gap solitons

We study quantum-noise squeezing and quantum correlations of gap solitons in a Bose-Einstein condensate loaded into a one-dimensional optical lattice. By employing a linearized quantum theory we find that quantum-noise squeezing of gap solitons, produced during their evolution, is enhanced compared with the atomic solitons in a lattice-free case due to intrasoliton structure of quantum correlations induced by the Bragg scattering in the periodic potential. We also show that nonlinear interaction of gap solitons in dynamically stable bound states can produce strong atom-number correlation between the soliton pairs.

Quantum noise properties of parametric processes

In this paper the quantum noise properties of phase-insensitive and phase-sensitive parametric processes are studied. Formulas for the field-quadrature and photon-number means and variances are derived, for processes that involve arbitrary numbers of modes. These quantities determine the signal-to-noise ratios associated with the direct and homo-dyne detection of optical signals. The consequences of the aforementioned formulas are described for frequency conversion, amplification, monitoring, and transmission through sequences of attenuators and amplifiers.

Quantum noise management in multi-element laser diode arrays

A theoretical analysis is performed of the quantum noise properties of multi-element laser diode arrays. A general formalism is presented which facilitates the estimation of the quantum noise arising due to cross contamination between lasing modes of the array. By consideration of three-element laser arrays a specific strategy is advanced for effecting quantum noise management in laser diode arrays.

Quantum noise properties of parametric amplifiers driven by two pump waves

In a parametric amplifier (PA) driven by two pump waves the signal sideband is coupled to three idler sidebands, all of which are frequency-converted (FC) images of the signal, and two of which are phaseconjugated (PC) images of the signal. If such a device is to be useful, the signal must be amplified, and the PC and FC idlers must be produced, with minimal noise. In this paper the quantum noise properties of two-sideband (TS) parametric devices are reviewed and the properties of many-sideband devices are determined. These results are applied to the study of two-pump PAs, which are based on the aforementioned four-sideband (FS) interaction. As a general guideline, the more sidebands that interact, the higher are the noise levels. However, if the pump frequencies are tuned to maximize the frequency bandwidth of the FS interaction, the signal and idler noise-figures are only slightly higher than the noise figures associated with the limiting TS interactions.

Investigations of the fundamental quantum noise properties of resonant-cavity light-emitting diodes (rcleds)

We present first results of the investigations of the quantum noise properties of resonant-cavity light-emitting diodes (rcleds). We obtain a quantum noise of up to −0.07dB below the shot noise quantum limit already at moderate pump levels and when being pumped by a quiet current source. This amount of observed sub-shot noise emission is in accordance with the quantum efficiency of the devices. This Sub-Poisson intensity noise ofrcleds together with their narrow beam characteristics make them very attractive for applications in photonics and metrology.

High-efficiency blue-light generation by frequency doubling of picosecond pulses in a thick KNbO_3 crystal

We report an experimental demonstration of highly efficient single-pass second-harmonic generation from 859 nm to 429.5 nm with picosecond pulses in a thick KNbO3 crystal. Both the conversion-efficiency and quantum-noise properties of the generated blue pulses are measured at various pump intensities under a strong focusing condition. We find that the variation of the conversion efficiency of the picosecond second-harmonic generation is an oscillatory function of the input pump intensity (with a maximum efficiency of 56.5%) and is sensitive to the position of the input beam focus in the crystal. The quantum noise on the blue beam can be reduced below the shot-noise limit by 20% at low input power.