Amount Of Squeezing Research Articles

Simulation of quantum optics by coherent state decomposition

We introduce a framework for simulating quantum optics by decomposing the system into a finite rank (number of terms) superposition of coherent states. This allows us to define a resource theory, where linear optical operations are “free” (i.e., do not increase the rank), and the simulation complexity for an m-mode system scales quadratically in m, in stark contrast to the Hilbert space dimension. We outline this approach explicitly in the Fock basis, relevant in particular for Boson sampling, where the simulation time (space) complexity for computing output amplitudes, to arbitrary accuracy, scales as O(m2 2 n ) [O(m2 n )] for n photons distributed among m modes. We additionally demonstrate that linear optical simulations with the n photons initially in the same mode scales efficiently, as O(m2 n). This paradigm provides a practical notion of “non-classicality,” i.e., the classical resources required for simulation. Moreover, by making connections to the stellar rank formalism, we show this comes from two independent contributions, the number of single-photon additions and the amount of squeezing.

Investigation of Stent Prototypes for the Eustachian Tube in Human Donor Bodies.

Chronic otitis media is often connected to Eustachian tube dysfunction. As successful treatment cannot be guaranteed with the currently available options, the aim is to develop a stent for the Eustachian tube (ET). Over the course of this development, different prototypes were generated and tested in ex vivo experiments. Four different prototypes of an ET stent and one commercially available coronary stent were implanted in the ET of seven human donor bodies. The position of the stents was verified by cone beam CT. The implanted ETs were harvested, embedded in resin and ground at 200 µm steps. Resulting images of the single steps were used to generate 3D models. The 3D models were then evaluated regarding position of the stent in the ET, its diameters, amount of squeezing, orientation of the axes and other parameters. Virtual reconstruction of the implanted ET was successful in all cases and revealed one incorrect stent placement. The cross-section increased for all metal stents in direction from the isthmus towards the pharyngeal orifice of the ET. Depending on the individual design of the metal stents (open or closed design), the shape varied also between different positions along a single stent. In contrast, the cross-section area and shape remained constant along the polymeric prototype. With the current investigation, insight into the behavior of different prototypes of ET stents was gained, which can help in defining the specifications for the intended ET stent.

Quantum-enhanced Doppler lidar

We propose a quantum-enhanced lidar system to estimate a target’s radial velocity, which employs squeezed and frequency-entangled signal and idler beams. We compare its performance against a classical protocol using a coherent state with the same pulse duration and energy, showing that quantum resources provide a precision enhancement in the estimation of the velocity of the object. We identify three distinct parameter regimes characterized by the amount of squeezing and frequency entanglement. In two of them, a quantum advantage exceeding the standard quantum limit is achieved assuming no photon losses. Additionally, we show that an optimal measurement to attain these results in the lossless case is frequency-resolved photon counting. Finally, we consider the effect of photon losses for the high-squeezing regime, which leads to a constant factor quantum advantage higher than 3 dB in the variance of the estimator, given a roundtrip lidar-to-target-to-lidar transmissivity larger than 50%.

Two-Mode Squeezed and Entangled Light Production in Parametric Oscillations

We investigate the statistical and quadrature squeezings, as well as the entanglement properties, of a two-mode light generated by non-degenerate parametric oscillations coupled to a two-mode squeezed vacuum reservoir, by employing the solutions of the quantum Langevin equations. It is found that the two-mode light shows the two-mode squeezing and entanglement for all values of the time. Moreover, it is observed that the squeezed vacuum reservoir and the growing amplitude of the pump mode enhance the degrees of two-mode squeezing and entanglement. We have also shown that the amounts of squeezing and entanglement are significant in a region, where the mean photon number is higher, and the photon number correlation is lower.

Spatiotemporal effects on squeezing measurements

The role of the spatiotemporal degrees of freedom in the preparation and observation of squeezed photonic states, produced by parametric down-conversion, is investigated. The analysis is done with the aid of a functional approach under the semi-classical approximation and the thin-crystal approximation. It is found that the squeezed state loses its minimum uncertainty property as the efficiency of down-conversion is increased, in a way that depends on the conditions of the homodyne measurements with which the amount of squeezing is determined.

Strong mechanical squeezing in a standard optomechanical system by pump modulation

Being beneficial for the amplitude modulation of the pump laser, we propose a simple yet surprisingly effective mechanical squeezing scheme in a standard optomechanical system. By merely introducing a specific kind of periodic modulation into the single-tone driving field to cool down the mechanical Bogoliubov mode, the far beyond 3-dB strong mechanical squeezing can be engineered without requiring any additional techniques. Specifically, we find that the amount of squeezing is not simply dependent on the order of magnitude of the effective optomechanical coupling but strongly on the ratio of sideband strengths for it. To maximize the mechanical squeezing, we numerically and analytically optimize this ratio in the steady-state regime, respectively. The mechanical squeezing engineered in our scheme also has strong robustness and can survive at a high bath temperature. Compared with previous schemes based on the two-tone pump technique, our scheme involves fewer external control laser source and can be extended to other quantum systems to achieve strong squeezing effect.

Encoding qubits into oscillators with atomic ensembles and squeezed light

The Gottesman-Kitaev-Preskill (GKP) encoding of a qubit within an oscillator provides a number of advantages when used in a fault-tolerant architecture for quantum computing, most notably that Gaussian operations suffice to implement all single- and two-qubit Clifford gates. The main drawback of the encoding is that the logical states themselves are challenging to produce. Here we present a method for generating optical GKP-encoded qubits by coupling an atomic ensemble to a squeezed state of light. Particular outcomes of a subsequent spin measurement of the ensemble herald successful generation of the resource state in the optical mode. We analyze the method in terms of the resources required (total spin and amount of squeezing) and the probability of success. We propose a physical implementation using a Faraday-based quantum non-demolition interaction.

Atom-assisted quadrature squeezing of a mechanical oscillator inside a dispersive cavity

We present a hybrid optomechanical scheme to achieve dynamical squeezing of position quadrature of a mesoscopic mechanical oscillator, that can be externally controlled by classical fields. A membrane-in-the-middle set up is employed, in which an atom in $\Lambda$ configuration is considered to be trapped on either side of the membrane inside the cavity. We show that a considerable amount of squeezing (beyond the 3 dB limit) can be achieved that is not affected by the decay of the cavity and the spontaneous emission of the atom. Squeezing depends upon the initial preparation of atomic states. Further, a strong effective coupling between the atom and the oscillator can be attained by using large control fields that pump the atom and the cavity. Effect of thermal phononic bath on squeezing is studied in terms of the squeezing spectrum. The results are supported by the detailed analytical calculations.

Power of one qumode for quantum computation

Although quantum computers are capable of solving problems like factoring exponentially faster than the best-known classical algorithms, determining the resources responsible for their computational power remains unclear. An important class of problems where quantum computers possess an advantage is phase estimation, which includes applications like factoring. We introduce a new computational model based on a single squeezed state resource that can perform phase estimation, which we call the power of one qumode. This model is inspired by an interesting computational model known as deterministic quantum computing with one quantum bit (DQC1). Using the power of one qumode, we identify that the amount of squeezing is sufficient to quantify the resource requirements of different computational problems based on phase estimation. In particular, it establishes a quantitative relationship between the resources required for factoring and DQC1. For example, we find the squeezing required to factor has an exponential scaling whereas no squeezing (i.e., a coherent state) is already sufficient to solve the hardest problem in DQC1.

The interaction between a single two-level atom and the combination of a frequency converter and the sub-harmonic generation

The problem of a time-dependent quantum system, which consists of coupled sub-harmonic generation with the parametric down conversion injected within a single cavity containing an atom, is considered. The problem is transformed into the interaction between the su(1,1) quantum system and a single two-level atom. The wave function is calculated and the expectation values for the dynamical operators are obtained. It is shown that the phenomenon of collapses and revivals are sensitive to the variation of the Bargmann index k and the Perelomov parameter η; moreover, a coherent trapping behavior is seen at the atomic coherence angle θ = π/2. The phenomena of bunching and anti-bunching are reported where the atomic angle θ and the phase angle φ as well as η are the most effective parameters. They are also effective for the variance squeezing, however the Bargmann index k increases the fluctuations and decreases the amount of squeezing. For the linear entropy we have observed that the index k has no effect, but the main effective parameters are θ, φ and η in addition to the ratio between the atomic frequency and the coupling parameter.

Grasping deformable planar objects: Squeeze, stick/slip analysis, and energy-based optimalities

Robotic grasping of deformable objects is difficult and under-researched, not simply due to the high computational cost of modeling. More fundamentally, several issues arise with the deformation of an object being grasped: a changing wrench space, growing finger contact areas, and pointwise varying contact modes inside these areas. Consequently, contact constraints needed for deformable modeling are hardly established at the beginning of the grasping operation. This paper presents a grasping strategy that squeezes the object with two fingers under specified displacements rather than forces. A ‘stable’ squeeze minimizes the potential energy for the same amount of squeezing, while a ‘pure’ squeeze ensures that the object undergoes no rigid body motion as it deforms. Assuming linear elasticity, a finite element analysis guarantees equilibrium and the uniqueness of deformation during a squeeze action. An event-driven algorithm tracks the contact regions as well as the modes of contact in their interiors under Coulomb friction, which in turn serve as the needed constraints for deformation update. Grasp quality is characterized as the amount of work performed by the grasping fingers in resisting a known push by some adversary finger. Simulation and multiple experiments have been conducted to validate the results over solid and ring-like 2D objects.

High-Fidelity Teleportation of Continuous-Variable Quantum States Using Delocalized Single Photons

Traditional continuous-variable teleportation can only approach unit fidelity in the limit of an infinite (and unphysical) amount of squeezing. We describe a new method for continuous-variable teleportation that approaches unit fidelity with finite resources. The protocol is not based on squeezed states as in traditional teleportation but on an ensemble of single photon entangled states. We characterize the teleportation scheme with coherent states, mesoscopic superposition states, and two-mode squeezed states and we find several situations in which near-unity teleportation fidelity can be obtained with modest resources.

N-ORDER SQUEEZING AND POISSONIAN STATISTICS OF A FOUR-LEVEL W-TYPE ATOM INTERACTING WITH ONE-MODE CAVITY FIELD

In this paper we consider a four-level W-type atom interacting with a single-mode quantized electromagnetic field in the presence of the Kerr medium. The atom and the field are initially prepared in the excited state and coherent state, respectively. The influence of the Kerr medium on the N-order squeezing and Poissonian statistics is investigated. We found that the maximum value of squeezing decreases by increasing the order N. Also, we noticed that the Kerr-like medium decreases the amount of squeezing and increases the sub-Poissonian statistics.

Squeezed state generation in photonic crystal microcavities

The feasibility of using a parametric down-conversion process to generate squeezed electromagnetic states in three dimensional photonic crystal microcavity structures is investigated for the first time. The spectrum of the squeezed light is theoretically calculated by using an open cavity quantum mechanical formalism. The cavity communicates with two main channels, which model vertical radiation losses and coupling into a single-mode waveguide respectively. The amount of squeezing is determined by the correlation functions relating the field quadratures of light coupled into the waveguide. All of the relevant model parameters are realistically estimated for structures made in Al0.3Ga0.7As, using finite-difference time-domain simulations. Squeezing up to approximately 30% below the shot noise level is predicted for 10 mW average power, 80 MHz repetition, 500 ps excitation pulses using in a [111] oriented wafer.

Optimized Double-Well Quantum Interferometry with Gaussian Squeezed States

A Mach-Zender interferometer with a Gaussian number-difference squeezed input state can exhibit sub-shot-noise phase resolution over a large phase interval. We derive the optimal level of squeezing for a given phase interval Deltatheta{0} and particle number N. We then propose an adaptive measurement sequence in which the amount of squeezing is increased with each measurement. With this scheme, any phase on (-Deltatheta{0},Deltatheta{0}) can be measured with a precision of 3.5/N, requiring only 2-4 measurements, provided only that Ntan(Deltatheta{0})<10{40}. In a double-well Bose-Einstein condensate, the optimized input states can be created by adiabatic manipulation of the ground state.

The role of squeezing in quantum key distribution based on homodyne detection and post-selection

The role of squeezing in quantum key distribution with continuous variables based on homodyne detection and post-selection is investigated for several specific eavesdropping attacks. It is shown that amplitude squeezing creates strong correlations between the signals of the legitimate receiver and a potential eavesdropper. Post-selection of the received pulses can therefore be used to reduce the eavesdropper's knowledge of the raw key, which increases the secret key rate by orders of magnitude over large distances even for modest amounts of squeezing.

The role of squeezing in quantum key distribution based on homodyne detection and post-selection

The role of squeezing in quantum key distribution with continuous variables based on homodyne detection and post-selection is investigated for several specific eavesdropping attacks. It is shown that amplitude squeezing creates strong correlations between the signals of the legitimate receiver and a potential eavesdropper. Post-selection of the received pulses can therefore be used to reduce the eavesdropper's knowledge of the raw key, which increases the secret key rate by orders of magnitude over large distances even for modest amounts of squeezing.

Statistics of polaritons in microcavities

We discuss the quantum statistical properties of exciton-polaritons in semiconductor microcavities. The nonlinear dynamics is treated within a model of interacting bosons for the signal, pump and idler modes. We focus on the regime of parametric amplification below threshold. We present the time evolution of the signal and idler modes towards their stationary solutions and evaluate the amount of squeezing of the radiation emitted out of the microcavity in a configuration, which is relevant for experiments. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Noise characteristics of oxide-confined vertical-cavity surface-emitting lasers

We demonstrate the possibility of generating intensity squeezed light with free-running or injected multimode vertical-cavity surface-emitting laser. Sub-shot-noise operation results from very strong anticorrelations between the transverse modes. The influence of the active media diameter on the amount of squeezing is analyzed.

Analysis of amplitude squeezing of harmonic generation in a quasi-phase-matched device: effect of stochastic variation of domain length

Amplitude squeezing of the second-harmonic generation in periodically poled quasi-phase-matched devices is analyzed with consideration for errors of the domain length. We show that the amount of squeezing is a complex function of the phase mismatch and of the input power and that it is practically impossible to maintain the perfect quasi-phase matching for an arbitrary input power. For evaluation of the availability of squeezing, we propose a contour map of squeezing that can visualize the tolerance of squeezing for the phase mismatch. It is shown that the effect of domain length error depends on the type of the error; the random duty-cycle error, where the mean domain period is precisely fixed, does not alter the squeezing performance, whereas the random period error, which fluctuates during the domain period, severely alters tuning characteristics. The available amount of squeezing is predicted to be determined by the tuning stability of the device.