Degenerate Optical Parametric Amplifier Research Articles

Multipartite continuous-variable entanglement from concurrent nonlinearities

We show theoretically that concurrent interactions in a second-order nonlinear medium placed inside an optical resonator can generate multipartite entanglement between the resonator modes. We show that there is a mathematical connexion between this system and van Loock and Braunstein's proposal for entangling N continuous quantum optical variables by interfering the outputs of N degenerate optical parametric amplifiers (OPA) at a N-port beam splitter. Our configuration, however, requires only one nondegenerate OPA and no interferometer. In a preliminary experimental study, we observe the concurrence of the appropriate interactions in periodically poled RbTiOAsO4.

Localization of optical wave packets by linear parametric amplification

It is revealed that simultaneous suppression of temporal and spatial spread of optical wave packets, which are free of angular dispersion can be achieved by linear parametric amplification. An effective suppression of beam diffraction in degenerate optical parametric amplifier is experimentally demonstrated. Good agreement of theoretical predictions with experimental results is obtained.

The solution of the Fokker-Planck equation of non-degenerate parametric amplific ation system for generation of squeezed light

In this paper, we present the analytical solution of the Fokker-Planck equation of non-degenerate optical parametric amplification(NOPA)for generation of squeezed light. The maximum intra-cavity compression of squeezed light derived from the analytical solution is 1/16(vacuum fluctuations 1/4). To compare it with that of the previous result 1/8 of degenerate optical parametric amplification(DOPA), it seems that the squeezing for NOPA is superior to the squeezing for DOPA.

Improved measurement of multimode squeezed light via an eigenmode approach

We analyze the output of a degenerate optical parametric amplifier using a different approach to understanding and characterizing multimode squeezed light. This approach is based on the concept of eigenmodes of the squeezing and predicts the mode structure of the local oscillator that should be used in order to measure the smallest quadrature noise. Although the importance of mode matching is well known, we find that typical experimental setups are suboptimal and we predict that in such cases squeezed light measurements stand to be improved noticeably with appropriate shaping (in space and/or time) of the local oscillator field in accordance with the results of the theory. Under conditions of negligible or small phase mismatch, the optimal local oscillator pulse duration is found to be approximately equal to the geometric mean of the pump pulse duration and nonlinear response time. Also, we find that the effective number of squeezed modes can be altered by varying the pump pulse duration and/or phase-matching parameters.

Influence of the randomly varying domain length of quasi-phase-matched crystals on quadrature squeezing performance

During the fabrication of quasi-phase-matched (QPM) devices, errors of periodic structure are usually inevitable. The errors result in the deviation of the actual periodic domain length from the theoretical value. In this paper, we numerically analyse the influence of errors on the quadrature squeezing performance of a degenerate optical parametric amplifier consisting of QPM devices. It is shown that errors significantly degrade the squeezing degree of the quadrature squeezed light. Due to the presence of the errors, the relative phase between the signal and the pump field for obtaining the maximum squeezing depends on the propagation distance of light in the crystal and the pump power.

Pulse compression and gain enhancement in a degenerate optical parametric amplifier based on aperiodically poled crystals

We describe theoretically a method of obtaining pulse compression and simultaneously improving amplification in a degenerate optical parametric amplifier by use of quasi-phase-matched engineered crystals. The scheme combines the possibility of increasing the signal spectral bandwidth that is offered by a degenerate parametric amplifier with the ability of engineered aperiodically poled crystals to compensate for group-velocity mismatch.

Analysis of the generation of amplitude-squeezed light with Gaussian-beam degenerate optical parametric amplifiers

We investigate the generation of amplitude-squeezed states with degenerate optical parametric amplifiers that are pumped by focused Gaussian beams. We present a model that facilitates the calculation of the squeezing level for an experimentally realistic configuration in which there is a Gaussian input signal beam that has the same confocal parameter and waist location as the Gaussian pump beam, with no restriction on the interaction length-to-confocal parameter ratio. We show that the 3-dB squeezing limit that was thought to be imposed by the Gaussian pump profile can be exceeded in the (previously uninvestigated) tight-focusing regime. We find the maximum possible amplitude squeezing in this regime to be 4.65 dB. However, it is possible to increase the squeezing level further by spatially filtering the tails of the output signal beam, resulting in squeezing levels in excess of 10 dB.

Amplification of Schrödinger-cat state in a degenerate optical parametric amplifier

Amplification of the Schrödinger-cat state (even coherent-state superposition) can be accompanied by its non-exponential decoherence and strong squeezing effect in the degenerate optical parametric amplifier. In the classical pump approximation and small thermal noise limit, the Wigner function behaviour illustrates that this non-exponential effect is induced by the phase-selective character of amplification. The non-exponential decoherence is much slower, in contrast with phase-unselective amplification exhibiting faster exponential decay. Thus, if one is able to produce the Schrödinger-cat state with at least a small amplitude, then it can be partially amplified with only a weak decoherence effect.

Analysis of Gaussian-beam degenerate optical parametric amplifiers for the generation of quadrature-squeezed states

This paper investigates the generation of quadrature-squeezed states of light using a degenerate optical parametric amplifier (DOPA) that is pumped by a focused Gaussian beam. The formulation that is presented facilitates the calculation of squeezing for an arbitrary local oscillator beam. This formulation also establishes a formal equivalence between the classical parametric gain and the measured level of squeezing. The maximum squeezing that can be achieved using a Gaussian-beam local oscillator is determined to be limited to 13.4 dB, as a consequence of gain-induced diffraction. The phase lag of the maximally squeezed quadrature is shown to be significantly different from the plane-wave theoretic value of $\ensuremath{\pi}/2,$ unless the focusing is very weak. The use of a second DOPA for generating a local oscillator beam that is matched to the squeezed field is also investigated. In this case, squeezing is limited only by the available pump power.

Coherence and complementarity in a Mach-Zehnder interferometer with two DOPAs

The characteristics of the quantum optical complementarity principle and the coherence of the photons generated in a Mach-Zehnder interferometer with two degenerate optical parametric amplifiers are analysed. The photon statistics and the phase fluctuation of the combined states are analysed in a homodyning Mach-Zehnder interferometer with two degenerate optical parametric amplifiers. By analysing the photon statistics, the mean-square phase fluctuation and the fringe visibility, the complementarity is considered as a function of the gain and input phase, when the amplified input is a coherent state containing one photon, on average. It is also considered when the input is a number state with one photon.

Properties of the linearized quantum optical bus

A formalism is developed that allows one to calculate the propagation of quantum noise, technical noise, and signals through a linearized quantum optical bus, i.e., a complex composite multibeam optical quantum system. General expressions for the output squeezing, the correlation coefficient, and quantum correlation coefficient between output observables and the transfer coefficients are derived and discussed in detail. The total correlation is introduced as a measure of the overall correlation of a set of output quadratures. From its geometric interpretation a multidimensional uncertainty relation is derived. Direct quantum-state preparation (QSP) is introduced as a method complementary to the conventional, indirect QSP. The minimal variance achievable by direct QSP is shown to provide superior noise suppression, including quantum noise suppression, than the conditional variance provided by indirect QSP. As an application we calculate and discuss the properties of a balanced bus of beam splitters with squeezed vacua at the usually unused ports. An important experimental effect is imperfect beam mode match, which is shown to lead to dramatic effects. A theory is derived which quantitatively matches measurements. Analytic expressions for the imperfectly modematched squeezed-light beam splitter including detection losses are given. Finally, a direct method is used to calculate the input-output matrix for the multiport subthreshold degenerate optical parametric amplifier for arbitrary parametric and mirror coupling strengths and detuning.

Generation of picosecond squeezed pulses using an all-solid-state cw mode-locked source

We have produced squeezed states of light using a degenerate optical parametric amplifier pumped by an all-solid-state cw mode-locked laser source. The process resulted in squeezed light pulses of less than 3 ps in duration. Up to 0.7 dB of amplitude-squeezed light at 1047 nm and 0.5 dB of noise reduction in vacuum were observed directly. The inferred squeezing level in both cases, after all propagation losses in the detection system and the effects of spatial and temporal mode overlap had been taken into account, was 1.8 dB.

Repeated Quantum Nondemolition Measurements of Continuous Optical Waves

Repeated quantum nondemolition (QND) measurements for continuous optical waves were performed by combining a degenerate optical parametric amplifier and a squeezed-light beam splitter. Two-step quantum state preparation and three-beam entanglement of the individually squeezed output beams were demonstrated. The experiment is analyzed using a set of generalized criteria for nonideal individual and repeated QND measurements. The system was operated fully stabilized for up to 36 hours. {copyright} {ital 1997} {ital The American Physical Society}

Optical phase stabilisation techniquefor pulsed degenerate optical parametric amplifiers

Tha authors present an optical phase control technique which does not use a dithering signal, and is suitable for pulsed interferometric systems. Implemented in a Q-switched mode-locked degenerate optical parametric amplifier, the control system is able to lock the optical intensity gain to within 1.7% error against random phase drift.

Quantum Nondemolition Measurements Improved by a Squeezed Meter Input

Continuous quantum nondemolition (QND) measurements of the amplitude quadrature of a 1064 nm wave are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). The quality of the measurement is limited in part by the quantum fluctuations carried by the vacuum meter input wave. Improved QND measurements are realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased squeezing and correlation of the output signal and meter waves, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for 5 h with high stability.

Continuous-wave quantum nondemolition measurements with vacuum and nonclassical meter input

QND measurements of the amplitude quadrature of continuous-wave light are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). Operated with a vacuum meter input, both output beams are squeezed and 33% correlated, demonstrating individually squeezed twin beams. The sum of the signal and meter transfer coefficients is 1.05, demonstrating operation as a quantum optical tap. The device exhibits quantum state preparation ability for both signal and meter output, reaching the conditional variances of \(-0.8\) dB and \(-2.5\) dB, respectively. An improved quantum measurement is realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased correlation and squeezing of the output beams, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for up to 5 hours with high stability.

Transformation of pulse characteristics via cascaded second-order effects in an optical parametric amplifier

We have demonstrated the linear transformation of a pulse chirp through second-order cascading in a degenerate phase-matched optical parametric amplifier by means of the self-diffraction process. We have measured as much as seven-fold enhancement of a frequency sweep rate in the diffracted idler pulses with no visible onset of intensity-dependent effects.

Bright squeezed-light generation by a continuous-wave semimonolithic parametric amplifier

Continuous-wave amplitude-squeezed light at 1064 nm has been generated with excellent long-term stability by use of a dual-port type I degenerate optical parametric amplifier pumped by a frequency-doubled Nd:YAG laser. A seed wave at 1064 nm is resonantly injected through the low-transmission cavity port, whereas the parametrically deamplified and squeezed output wave is extracted from the high-transmission port. Amplitude noise reduction of as much as 4.3 dB is observed directly at an output power of 0.15 mW. Stable noise suppression exceeding 3.8 dB is obtained for several hours by phase locking of the pump wave. The longterm stability and simplicity make this device suitable for sub-shot-noise metrology.

High-accuracy optical homodyne detection with low-efficiency detectors: "Preamplification" from antisqueezing.

A novel experimental scheme is proposed that allows us to avoid the deterioration of homodyne detection measurements due to nonideal detectors. The basic idea is to preamplify the signal by means of antisqueezing. Experimentally, we would employ a squeezer, e.g., a degenerate optical parametric amplifier, that squeezes just the nonobserved quadrature component of the electric field while antisqueezing the conjugate component which is measured. It is shown that for sufficiently strong antisqueezing one achieves the same measurement accuracy as with perfectly efficient detectors. In particular, in this way the actual Wigner function can be reconstructed in cptical homodyne tomography.

Deamplification response of a traveling-wave phase-sensitive optical parametric amplifier

We have investigated the phase-sensitive deamplification response of a traveling-wave degenerate optical parametric amplifier that consists of a type II phase-matched KTP crystal pumped by the second harmonic of a Q-switched mode-locked Nd:YAG laser. Experimental results are in good agreement with the theory of an optical parametric amplifier in which the Gaussian-beam nature of the various fields along with the diffraction of the amplified signal beam is taken into account. Because of the phenomenon of gain-induced diffraction, maximum deamplification is limited to only ≃3 dB.