Entanglement, Interference, and Measurement in a Degenerate Parametric Oscillator (original) (raw)

Testing the entanglement of intense beams produced by a non-degenerate optical parametric oscillator

Optics Communications, 2004

We propose a direct measurement of the quadrature correlations of signal and idler beams in a non-degenerate optical parametric oscillator operating above threshold. We investigate the experimental limits where quantum correlations can be observed, fulfilling an inseparability criterion for defining them as intense entangled beams. The use of optical cavities to access quadrature noise in this situation is studied, and its advantages over homodyne detection are discussed. We also consider the application of this entanglement and the quadrature noise measurement technique to quantum cryptography.

The Test of Entanglement of Polarization States of a Semi-Classical Optical Parametric Oscillator

American Journal of Modern Physics, 2017

We study the dynamical continuous variable entanglement in a semi-classical Optical parametric oscillator (OPO). The general time evolving photon polarization state vectors arising from exact analytical solutions of Heisenberg’s equations of the system are used to obtain the photon polarization Bell state vectors. The reduced density matrices of photon polarization Bell state vectors of the semi-classical OPO produce a greater violation of CHSH Bell’s inequality beyond the Cirel’son’s inequality.

Entanglement in the above-threshold optical parametric oscillator

Journal of the Optical Society of America B, 2007

We investigate entanglement in the above-threshold optical parametric oscillator, both theoretically and experimentally, and discuss its potential applications to quantum information. The fluctuations measured in the subtraction of signal and idler amplitude quadratures are ⌬ 2 p − = 0.50͑1͒, or −3.01͑9͒ dB, and in the sum of phase quadratures they are ⌬ 2 q + = 0.73͑1͒, or −1.37͑6͒ dB. A detailed experimental study of the noise behavior as a function of pump power is presented, and the discrepancies with theory are discussed.

Theory of photon statistics and squeezing in quantum interference of a sub-threshold parametric oscillator

Optics Express, 2003

A multimode theory describing quantum interference of a subthreshold optical parametric oscillator (OPO) with a coherent local oscillator (LO) in a homodyne detection scheme is presented. Analytic expressions for the count rates in terms of the correlation time and relative phase difference between the LO and OPO have been derived. The spectrum of squeezing is also derived and the threshold for squeezing obtained in terms of the crystal nonlinearity and LO and OPO beam intensities.

Detection of continuous variable entanglement without coherent local oscillators

Physical Review A, 2008

We propose three criteria for identifying continuous variable entanglement between two many-particle systems with no restrictions on the quantum state of the local oscillators used in the measurements. Mistakenly asserting a coherent state for the local oscillator can lead to incorrectly identifying the presence of entanglement. We demonstrate this in simulations with 100 particles, and also find that large number fluctuations do not prevent the observation of entanglement. Our results are important for quantum information experiments with realistic Bose-Einstein condensates or in optics with arbitrary photon states. PACS numbers: 03.67.Mn,03.75.Gg,03.65.Ud,42.50.Dv The study of the quantum properties of matter-waves is a rapidly developing field known as quantum atom optics . Already several experiments have observed non-classical effects in ultra-cold gases, including the Hanbury Brown-Twiss effect for bosons , anti-bunching for fermions , sub-Poissonian number fluctuations , and density correlations from molecular dissociation [6] and in the Mott-insulator regime in an optical lattice . Although impressive achievements, the experimental techniques utilized in these observations are insufficient to detect quantum squeezing or entanglement. The demonstration of entanglement -which Schrödinger described as being the central mystery of quantum mechanics [8] -will be an important step towards quantum information applications of ultra-cold atomic systems.

Generation of entanglement in quantum parametric oscillators using phase control

Scientific Reports, 2015

The control of quantum entanglement in systems in contact with environment plays an important role in information processing, cryptography and quantum computing. However, interactions with the environment, even when very weak, entail decoherence in the system with consequent loss of entanglement. Here we consider a system of two coupled oscillators in contact with a common heat bath and with a time dependent oscillation frequency. The possibility to control the entanglement of the oscillators by means of an external sinusoidal perturbation applied to the oscillation frequency has been theoretically explored. We demonstrate that the oscillators become entangled exactly in the region where the classical counterpart is unstable, otherwise when the classical system is stable, entanglement is not possible. Therefore, we can control the entanglement swapping from stable to unstable regions by adjusting amplitude and phase of our external controller. We also show that the entanglement rate is approximately proportional to the real part of the Floquet coefficient of the classical counterpart of the oscillators. Our results have the intriguing peculiarity of manipulating quantum information operating on a classical system.

Quantum nondemolition measurements of a qubit coupled to a harmonic oscillator

Physical Review B, 2009

We theoretically describe the weak measurement of a two-level system (qubit) and quantify the degree to which such a qubit measurement has a quantum non-demolition (QND) character. The qubit is coupled to a harmonic oscillator which undergoes a projective measurement. Information on the qubit state is extracted from the oscillator measurement outcomes, and the QND character of the measurement is inferred from the result of subsequent measurements of the oscillator. We use the positive operator valued measure (POVM) formalism to describe the qubit measurement. Two mechanisms lead to deviations from a perfect QND measurement: (i) the quantum fluctuations of the oscillator, and (ii) quantum tunneling between the qubit states |0 and |1 during measurements. Our theory can be applied to QND measurements performed on superconducting qubits coupled to a circuit oscillator.

Quantum images in non degenerate optical parametric oscillators

The European Physical Journal D, 2000

Quantum images, that is inhomogeneous field distributions purely generated by quantum fluctuations, persist when passing from the degenerate to the non-degenerate case of optical parametric oscillators (OPO). Below the threshold for parametric oscillation where the near-field distributions are homogeneous both in intensity and phase, appropriate spatial correlation functions anticipate the transverse spatial pattern that appears above threshold. In particular, the angular dependence of the far field spatial correlation function is able to reveal the travelling-wave nature of the phase pattern above threshold typical of nondegenerate OPOs. Cross-correlation functions between signal and idler intensities show clear evidence of the non-classical nature of the output light.

Quantum information processing and precise optical measurement with entangled-photon pairs

Contemporary Physics, 2003

Two photons in a pair generated in the nonlinear optical process of spontaneous parametric down-conversion are, in general, strongly quantum entangled. Accordingly, they contain extremely strong energy, time, polarization and momentum quantum correlations. This entanglement involves more than one quantum variable and has served as a powerful tool in fundamental studies of quantum theory. It is now playing a large role in the development of novel information processing techniques and new optical measurement technologies. Here we review some of these technologies and their origins.