We report on specific signatures of squeezing for time-modulated light fields. We show that application of periodically-modulated driving fields instead of continuous wave fields drastically improves the degree of quadrature integral squeezing in an optical parametric oscillator. These results particularly allow for applications in time-resolved quantum communication protocols.
We report generation of squeezed vacuum in sideband modes of continuous-wave light at 946 nm using a periodically poled KTiOPO_4 crystal in an optical parametric oscillator. At the pump power of 250 mW, we observe the squeezing level of -5.6+/-0.1 dB and the anti-squeezing level of +12.7+/-0.1 dB. The pump power dependence of the observed squeezing/anti-squeezing levels agrees with the theoretically calculated values when the phase fluctuation of locking is taken into account.
We study the process of squeezing of an ensemble of cold atoms in a pulsed optical lattice. The problem is treated both classically and quantum-mechanically under various thermal conditions. We show that a dramatic compression of the atomic density near the minima of the optical potential can be achieved with a proper pulsing of the lattice. Several strategies leading to the enhanced atomic squeezing are suggested, compared and optimized.
We observed -7.2 dB quadrature squeezing at 860 nm by using a sub-threshold continuous-wave pumped optical parametric oscillator with a periodically-poled KTiOPO4 crystal as a nonlinear optical medium. The squeezing level was measured with the phase of homodyne detection locked at the quadrature. The blue light induced infrared absorption was not observed in the experiment.
We generated -2.2 dB of broadband amplitude squeezing at 1064 nm in a periodically poled KTiOPO_4 (PPKTP) waveguide, by coupling of the fundamental and second harmonic continuous-wave fields. This is the largest amount of squeezing obtained to date in a KTP waveguide, limited by propagation losses. This result paves the way for further improvements by use of lower-loss buried ion-exchanged waveguides.
Achieving high level of pulsed squeezing, in a platform which offers integration and stability, is a key requirement for continuous-variable quantum information processing. Typically highly squeezed states are achieved with narrow band optical cavities and bulk crystals, limiting scalability. Using single-pass parametric down conversion in an integrated optical device, we demonstrate quadrature squeezing of picosecond pulses in a thin-film lithium niobate strip-loaded waveguide. For on-chip peak powers of less than 0.3 W, we measure up to -0.33$\pm$0.07 dB of squeezing with an inferred on-chip…
We analyze the spectral properties of squeezed light produced by means of pulsed, single-pass degenerate parametric down-conversion. The multimode output of this process can be decomposed into characteristic modes undergoing independent squeezing evolution akin to the Schmidt decomposition of the biphoton spectrum. The main features of this decomposition can be understood using a simple analytical model developed in the perturbative regime. In the strong pumping regime, for which the perturbative approach is not valid, we present a numerical analysis, specializing to the case of one-dimensiona…
Mesoscopic mechanical oscillators can be prepared in quantum states and coherently manipulated using the optomechanical interaction. This has recently been used to prepare squeezed mechanical states. However, the scheme used in these experiments relies on slow, dissipative evolution that destroys the system's memory of its initial state. In this paper we propose a protocol based on a sequence of four pulsed optomechanical interactions. In addition to being coherent, our scheme executes in a time much shorter than a mechanical period. We analyse applications in impulsive force sensing and prese…
We present experimental studies on the generation of pulsed and continuous-wave squeezed vacuum via nonlinear rotation of the polarization ellipse in a $^{87}$Rb vapor. Squeezing is observed for a wide range of input powers and pump detunings on the D1 line, while only excess noise is present on the D2 line. The maximum continuous-wave squeezing observed is -$ 1.4 \pm0.1$ dB (-2.0 dB corrected for losses). We measure -1.1 dB squeezing at the resonance frequency of the $^{85}$Rb $F=3 \to F'$ transition, which may allow the storage of squeezed light generated by $^{87}$Rb in a $^{85}$Rb quantum …
In this paper, we demonstrate efficient generation of collinearly propagating, degenerate pulsed photon pairs based on a bulk Periodically Poled Potassium Titanyl Phosphate pumped by an ultrashort pulse laser. Using a single-mode fiber as a spatial mode filter, we detect about 3200 coincidence counts per second per milliwatt pump power. After we consider main losses in our experiment, the inferred coincidence counts are about 109000 per second per milliwatt pump power. This is the very promising for realization of sources for quantum communication and metrology.
We report the experimental demonstration of directly produced polarization squeezing at 1064 nm from a type I optical parametric amplifier (OPA) based on a periodically poled KTP crystal (PPKTP). The orthogonal polarization modes of the polarization squeezed state are both defined by the OPA cavity mode, and the birefringence induced by the PPKTP crystal is compensated for by a second, but inactive, PPKTP crystal. Stokes parameter squeezing of 3.6 dB and anti squeezing of 9.4 dB is observed.
We demonstrate a quantum regime of dissipative nonlinear oscillator where creation of Fock states as well as superpositions of Fock states are realized for time-intervals exceeding the characteristic decoherence time. Preparation of quantum states is conditioned by strong Kerr nonlinearity as well as by excitation of resolved lower oscillatory energy levels with specific train of Gaussian pulses. This provides practical signatures to look for in experiments with cooled nonlinear oscillators.
Squeezed light has evolved into a powerful tool for quantum technology, ranging from quantum enhanced sensing and quantum state engineering based on partial post-selection techniques. The pulsed generation of squeezed light is of particular interest, as it can provide accurate time stamp and physically defined temporal mode, which are highly preferred in complex communication networks and large-scale information processing. However, the multimode feature of pulsed squeezing in conventional single-pass configuration limits the purity of the output state, negatively impacting its application in …
We discuss the concept of characteristic squeezing modes applied to a travelling-wave optical parametric amplifier pumped by an ultrashort pulse. The characteristic modes undergo decoupled single-mode squeezing transformations, and therefore they form a useful basis to describe the evolution of the entire multimode system. This provides an elegant and intuitive picture of quantum statistical properties of parametric fluorescence. We analyse the efficiency of detecting quadrature squeezing, and present results of numerical calculations for a realistic nonlinear medium.
We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counter-propagating coherent states are ejected from the centre of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the Quantum Kicked Rotor (QKR). From this we can analyse the entanglement production and interpret the ejected coherent states as a manifestation of so-called `accelerator modes' o…
We study the emergence of non-Gaussian quantum features in pulsed squeezed light generation with a mesoscopic number (i.e., dozens to hundreds) of pump photons. Due to the strong optical nonlinearities necessarily involved in this regime, squeezing occurs alongside significant pump depletion, compromising the predictions made by conventional semiclassical models for squeezing. Furthermore, nonlinear interactions among multiple frequency modes render the system dynamics exponentially intractable in naïve quantum models, requiring a more sophisticated modeling framework. To this end, we construc…
We report generation of a continuous-wave squeezed vacuum resonant on the Rb D_1 line (795 nm) using periodically poled KTiOPO_4 (PPKTP) crystals. With a frequency doubler and an optical parametric oscillator based on PPKTP crystals, we observed a squeezing level of -2.75 +- 0.14 dB and an anti-squeezing level of +7.00 +- 0.13 dB. This system could be utilized for demonstrating storage and retrieval of the squeezed vacuum, which is important for the ultra-precise measurement of atomic spins as well as quantum information processing.
Hybrid quantum information processing combines the advantages of discrete and continues variable protocols by realizing protocols consisting of photon counting and homodyne measurements. However, the mode structure of pulsed sources and the properties of the detection schemes often require the use optical filters in order to combine both detection methods in a common experiment. This limits the efficiency and the overall achievable squeezing of the experiment. In our work, we use photon subtraction to implement the distillation of pulsed squeezed states originating from a genuinely spatially a…
We systematically study the influence of amplitude modulation on the steady-state bosonic squeezing and entanglement in a dissipative three-mode optomechanical system, where a vibrational mode of the membrane is coupled to the left and right cavity modes via the radiation pressure. Numerical simulation results show that the steady-state bosonic squeezing and entanglement can be significantly enhanced by periodically modulated external laser driving either or both ends of the cavity. Remarkably, the fact that as long as one periodically modulated external laser driving either end of the cavitie…
We investigate the dynamics of an optomechanical system where a cavity with a movable mirror involves a degenerate optical parametric amplifier and is driven by a periodically modulated laser field. Our results show that the cooperation between the parametric driving and periodically modulated cavity driving results in a two-fold squeezing on the movable cavity mirror that acts as a mechanical oscillator. This allows the fluctuation of the mechanical oscillator in one quadrature (momentum or position) to be reduced to a level that cannot be reached by solely applying either of these two drivin…
Generation of mechanical squeezing has attracted a lot of interest for its nonclassical properties, applications in quantum information, and high-sensitivity measurement. Here we propose a detuning-switched method that can rapidly generate strong and stationary mechanical squeezing. The pulsed driving can dynamically transpose the optomechanical coupling into a linear optical force and maintain an effective mechanical frequency, which can introduce strong mechanical squeezing in a short time. Moreover, we show the obtained strong mechanical squeezing can be frozen by increasing the pulse inter…
Direct photon detection is experimentally implemented to measure the squeezing and purity of a single-mode squeezed vacuum state without an interferometric homodyne detection. Following a recent theoretical proposal [arXiv quant-ph/0311119], the setup only requires a tunable beamsplitter and a single-photon detector to fully characterize the generated Gaussian states. The experimental implementation of this procedure is discussed and compared with other reference methods.
We consider a system consisting of a single two-level ion in a harmonic trap, which is localized inside a non-ideal optical cavity at zero temperature and subjected to the action of two external lasers. We are able to obtain an analytical solution for the total density operator of the system and show that squeezing in the motion of the ion and in the cavity field is generated. We also show that complete revivals of the states of the motion of the ion and of the cavity field occur periodically.
Quantum pulsed second-subharmonic generation in a planar waveguide with a small periodic corrugation at the surface is studied. Back-scattering of the interacting fields on the corrugation enhances the nonlinear interaction giving larger values of squeezing. The problem of back-scattering is treated by perturbation theory, using the Fourier transform for non-dispersion propagation, and by numerical approach in the general case. Optimum spectral modes for squeezed-light generation are found using the Bloch-Messiah reduction. Improvement in squeezing and increase of numbers of generated photons …
We report the realization of a bright ultrafast two-mode squeezer based on type II parametric downconversion (PDC) in periodically poled $\mathrm{KTiOPO_4}$ (PP-KTP) waveguides. It produces a pulsed two-mode squeezed vacuum state: a photon-number entangled pair of truly single-mode pulses or, in terms of continuous variables quantum optics, a pulsed, single mode Einstein-Podolsky-Rosen (EPR) state in the telecom regime. We prove the single mode character of our source by measuring its $g^{(2)}$ correlation function and demonstrate a mean photon number of up to 2.5 per pulse, equivalent to 11dB…
We demonstrate vacuum squeezing at the D1 line of atomic rubidium (795 nm) with a tunable, doubly-resonant, monolithic sub-threshold optical parametric oscillator in periodically-poled Rb-doped potassium titanyl phosphate. The squeezing appears to be undiminished by a strong dispersive optical nonlinearity recently observed in this material.
We consider pulsed-pump spontaneous parametric downconversion (SPDC) as well as pulsed single- and dual-pump spontaneous four-wave mixing processes in waveguides within a unified Hamiltonian theoretical framework. Working with linear operator equations in $k$-space, our approach allows inclusion of linear losses, self- and cross-phase modulation, and dispersion to any order. We describe state evolution in terms of second-order moments, for which we develop explicit expressions. We use our approach to calculate the joint spectral amplitude of degenerate squeezing using SPDC analytically in the …
We study the spectral properties of Spontaneous Parametric Down Conversion in a periodically poled waveguided structure of KTP crystal pumped by ultra-short pulses. Our theoretical analysis reveals a strongly multimode and asymmetric structure of the two-photon spectral amplitude for type-II SPDC. Experimental evidence, based on Hong-Ou-Mandel polarization interference with narrowband filtering, confirms this result.
Squeezing is a resource that enables precision enhancements in quantum metrology and can be used as a basis for the generation of entanglement by linear optics. While strong squeezing is challenging to generate in optical fields, here we present simple periodic modulation protocols in optomechanical systems that can generate large squeezing of their mechanical degrees of freedom for realistic system parameters. We then proceed to show how such protocols can serve to improve the measurement precision of weak forces and enhance the generation of entanglement between test masses that are subject …
We report on effective generation of continuous-wave squeezed light and second harmonics with a periodically poled MgO:LiNbO$_{\mathrm{3}}$ (PPMgLN) crystal which enables us to utilize the large nonlinear optical coefficient $d_{\mathrm{33}}$. We achieved the squeezing level of $-7.60 \pm 0.15$dB at 860 nm by utilizing a subthreshol optical parametric oscillator with a PPMgLN crystal. We also generated 400 mW of second harmonics at 430 nm from 570 mW of fundamental waves with 70% of conversion efficiency by using a PPMgLN crystal inside an external cavity.
We report on the generation of a stable continuous-wave low-frequency squeezed vacuum field with a squeezing level of $3.8\pm0.1$ dB at 1064 nm, the wavelength at which laser interferometers for gravitational wave (GW) detection operate, using periodically poled KTiOPO$_4$ (PPKTP) in a sub-threshold optical parametric oscillator. PPKTP has the advantages of higher nonlinearity, smaller intra-crystal and pump-induced seed absorption, user-specified parametric down-conversion temperature, wider temperature tuning range, and lower susceptibility to thermal lensing over alternative nonlinear mater…
Continuous-wave squeezed states of light at the wavelength of 1550 nm have recently been demonstrated, but so far the obtained factors of noise suppression still lag behind today's best squeezing values demonstrated at 1064 nm. Here we report on the realization of a half-monolithic nonlinear resonator based on periodically-poled potassium titanyl phosphate which enabled the direct detection of up to 12.3 dB of squeezing at 5 MHz. Squeezing was observed down to a frequency of 2 kHz which is well within the detection band of gravitational wave interferometers. Our results suggest that a long-ter…
All-optical switching used to switch the input optical signals without any electro-optical conversion plays a vital role in the next generation of optical information processing devices. Even all-optical switchings (AOSs) with continuous input signals have been widely studied, all-optical pulse switchings (AOPSs) whose input signals are pulse sequences have rarely been investigated because of the time-dependent Hamiltonian, especially for dissipative quantum systems. In this paper, we propose an AOPS scheme, where a strong pulsed field is used to switch another pulsed input signal. With the he…
We have constructed a pulsed laser system for the manipulation of cold Rb atoms. The system combines optical telecommunications components and frequency doubling to generate light at 780 nm. Using a fast, fibre-coupled intensity modulator, output from a continuous laser diode is sliced into pulses with a length between 1.3 and 6.1 ns and a repetition frequency of 5 MHz. These pulses are amplified using an erbium-doped fibre amplifier, and frequency-doubled in a periodically poled lithium niobate crystal, yielding a peak power up to 12 W. Using the resulting light at 780 nm, we demonstrate Rabi…
We report a source of polarization-entangled photon pairs in the 1550-nm telecommunication band, which is based on non-collinear spontaneous parametric down-conversion in a periodically poled lithium niobate crystal pumped by picosecond pulses. This source is realized utilizing a polarization-based Sagnac interferometer employing a type-0 non-collinear quasi-phase-matching configuration. Polarization entanglement is verified through measurement of the polarization-correlation interference fringes with visibility >96% and by testing the experimental violation of the Clauser-Horne-Shimony-Holt (…
We report on efficient generation of second harmonic laser and single-mode vacuum squeezed light of 795 nm with periodically poled KTiOPO4 (PPKTP) crystals. We achieved 111 mW of ultra-violet (UV) light at 397.5 nm from 191 mW of fundamental light with a PPKTP crystal in a doubling cavity, corresponding to a conversion efficiency of 58.1%. Using the UV light to pump an optical parametric oscillator with a PPKTP crystal, we realized -5.6 dB of a maximum squeezing. We analyzed the pump power dependence of the squeezing level and concluded that the UV light induced losses limit the improvement of…
We study the Bloch-Messiah reduction of parametric downconversion of light in the pulsed regime with a nondegenerate phase matching providing generation of twin beams. We find that in this case every squeezing eigenvalue has multiplicity at least two. We discuss the problem of ambiguity in the definition of the squeezing eigenmodes in this case and develop two approaches to unique determination of the latter. First, we show that the modal functions of the squeezing eigenmodes can be tailored from the Schmidt modes of the signal and idler beams. Alternatively, they can be found as a solution of…
We investigate the influence of periodically time-modulated cavity frequency on the generation of atomic squeezed states for a collection of N two-level atoms confined in a non-stationary cavity with a moving mirror. We show that the two-photon character of the field generated from the vacuum state of field plays a significant role in producing the atomic or spin squeezed states. We further show that the maximum amount of persistent atomic squeezing is obtained for the initial cavity field prepared in the vacuum state.
A growing number of experimental set-ups in cavity optomechanics exploit periodically driven fields. However, such set-ups are not amenable to analysis using simple, yet powerful, closed-form expressions of linearized optomechanics, which have provided so much of our present understanding of experimental optomechanics. In the present paper, we formulate a new method to calculate quantum noise spectra in modulated optomechanical systems, which we analyze, compare, and discuss with two other recently proposed solutions: we term these (i) frequency-shifted operators (ii) Floquet and (iii) iterati…
We present a simple quantum theory for the pulsed light generated by a synchronously pumped optical parametric oscillator (SPOPO) in the degenerate case where the signal and idler trains of pulses coincide, below threshold and neglecting all dispersion effects. Our main goal is to precise in the obtained quantum effects, which ones are identical to the c.w. case and which ones are specific to the SPOPO. We demonstrate in particular that the temporal correlations have interesting peculiarities: the quantum fluctuations at different times within the same pulse turn out to be totally not correlat…
Squeezed states can be employed for entanglement-based continuous-variable quantum key distribution, where the secure key rate is proportional to the bandwidth of the squeezing. We produced a non-classical continuous-wave laser field at the telecommunication wavelength of 1550 nm, which showed squeezing over a bandwidth of more than 2 GHz. The experimental setup used parametric down-conversion via a periodically poled potassium titanyl phosphate crystal (PPKTP). We did not use any resonant enhancement for the funda- mental wavelength, which should in principle allow a production of squeezed li…
Amplitude squeezed pulsed light has been produced using a microstructured silica fibre. By spectrally filtering after the nonlinear propagation in the fibre a squeezing value of -1.7dB has been measured. A quantum key distribution scheme based on squeezed light from such microstructured fibres is proposed.
Semiclassical catastrophes in the dynamics of a quantum rotor (molecule) driven by a strong time-varying field are considered. We show that for strong enough fields, a sharp peak in the rotor angular distribution can be achieved via time-domain focusing phenomenon, followed by the formation of angular rainbows and glory-like angular structures. Several scenarios leading to the enhanced angular squeezing are proposed that use specially designed and optimized sequences of pulses. The predicted effects can be observed in many processes, ranging from molecular alignment (orientation) by laser fiel…
We report the simultaneous quasi-phase-matching of all three possible nonlinearities for propagation along the X axis of periodocally poled (PP) KTiOPO4 (KTP) for second-harmonic generation of 745 nm pulsed light from 1490nm subpicosecond pulses in a PPKTP crystal with a 45.65 micrometer poling period. This confirms the recent Sellmeier fits of KTP by K. Kato and E. Takaoka [Appl. Opt. 41, 5040 (2002)]. Such coincident nonlinearities are of importance for realizing compact sources of multipartite continuous-variable entanglement [Pfister et al., Phys. Rev. A 70, 020302 (2004)] and we propose a…
We theoretically investigate the generation of two entangled beams of light in the process of single-pass type-I noncollinear frequency degenerate parametric downconversion with an ultrashort pulsed pump. We find the spatio-temporal squeezing eigenmodes and the corresponding squeezing eigenvalues of the generated field both numerically and analytically. The analytical solution is obtained by modeling the joint spectral amplitude of the field by a Gaussian function in curvilinear coordinates. We show that this method is highly efficient and is in a good agreement with the numerical solution. We…
We consider multiple-period states in systems of periodically modulated qubits. In such states the discrete time-translation symmetry imposed by the modulation is broken. We explicitly show how multiple-period states emerge in the simplest quantum system, a single qubit subjected to a pulsed resonant modulation and/or a pulsed modulation of the transition frequency. We also show that a qubit chain with the qubit coupling modulated at twice the qubit frequency has symmetry that allows mapping it on the Kitaev chain and thus provides an example of a topologically nontrivial Floquet system. An ex…
We present theoretical and experimental results on the generation and detection of pulsed, relative-intensity squeezed light in a hot Rb87 vapor. The intensity noise correlations between a pulsed probe beam and its conjugate, generated through nearly-degenerate four-wave mixing in a double-lambda system, are studied numerically and measured experimentally via time-resolved balanced detection. We predict and observe about -1 dB of time-resolved relative intensity squeezing with 50 nanosecond pulses at 1 MHz repetition rate. (-1.34 dB corrected for loss).
The emergence of parity-time ($\mathcal{PT}$) symmetry has greatly enriched our study of symmetry-enabled non-Hermitian physics, but the realization of quantum $\mathcal{PT}$-symmetry faces an intrinsic issue of unavoidable symmetry-breaking Langevin noises. Here we construct a quantum pseudo-anti-$\mathcal{PT}$ (pseudo-$\mathcal{APT}$) symmetry in a two-mode bosonic system without involving Langevin noises. We show that the spontaneous pseudo-$\mathcal{APT}$ symmetry breaking leads to an exceptional point, across which there is a transition between different types of quantum squeezing dynamic…