Single Homodyne Detector Research Articles

Reconstructing Gaussian bipartite states with a single polarization-sensitive homodyne detector.

We present a novel method to fully estimate Gaussian bipartite polarization states using only a single homodyne detector. Our approach is based on [Phys. Rev. Lett.102, 020502 (2009)10.1103/PhysRevLett.102.020502], but circumvents additional optics, and thereby losses, in the signal path. We provide an intuitive explanation of our scheme without needing to define auxiliary modes. With six independent measurements, we fully reconstruct the state's covariance matrix. We validate our method by comparing it to a conventional dual-homodyne measurement scheme.

Free-space continuous-variable quantum key distribution of unidimensional Gaussian modulation using polarized coherent states in an urban environment

We use single homodyne detector to accomplish Continuous-Variable quantum key distribution(CV QKD) in a laboratory and urban environment free-space channel. This is based on Gaussian modulation with coherent-states in the polarization degree of freedom. We achieved a QKD distance at 460m, at the repetition rate of 10 kHz. We give the security of this protocol against collective attack in the asymptotic regime. The secure key rate is 0.152 kbps at the typical reconciliation efficiency of 0.95. The experiment setup of this scheme is simplified and the difficulty to realize has been remarkably reduced compared to traditional symmetric modulation ones, for example, GG02 protocol. The influence of security key rate brought by asymmetric modulation is small in a relative low channel loss condition in the free-space environment. This scheme is expected to be significance meaning to the future practically utilize.

Homodyning the [formula omitted] of Gaussian states

We suggest a method to reconstruct the zero-delay-time second-order correlation function g(2)(0) of Gaussian states using a single homodyne detector. To this purpose, we have found an analytic expression of g(2)(0) for single- and two-mode Gaussian states in terms of the elements of their covariance matrix and the displacement amplitude. In the single-mode case we demonstrate our scheme experimentally, and also show that when the input state is nonclassical, there exist a threshold value of the coherent amplitude, and a range of values of the complex squeezing parameter, above which g(2)(0)<1. For amplitude squeezing and real coherent amplitude, the threshold turns out to be a necessary and sufficient condition for the nonclassicality of the state. Analogous results hold also for two-mode squeezed thermal states.

Full quantum state reconstruction of symmetric two-mode squeezed thermal states via spectral homodyne detection and a state-balancing detector

We suggest and demonstrate a scheme to reconstruct the symmetric two-mode squeezed thermal states of spectral sideband modes from an optical parametric oscillator. The method is based on a single homodyne detector and active stabilization of the cavity. The measurement scheme have been successfully tested on different two-mode squeezed thermal states, ranging from uncorrelated coherent states to entangled states.

Experimental analysis of decoherence in continuous-variable bipartite systems

Quantum properties are soon subject to decoherence once the quantum system interacts with the classical environment. In this paper we experimentally test how propagation losses, in a Gaussian channel, affect the bipartite Gaussian entangled state generated by a subthreshold type-II optical parametric oscillator. Experimental results are discussed in terms of different quantum markers, as teleportation fidelity, quantum discord, and mutual information, and continuous-variable (CV) entanglement criteria. To analyze state properties we have retrieved the composite system covariance matrix by a single homodyne detector. We experimentally found that, even in the presence of a strong decoherence, the generated state never disentangles and keeps breaking the quantum limit for the discord. This result proves that the class of CV entangled states discussed in this paper would allow, in principle, to realize quantum teleportation over an infinitely long Gaussian channel.

Characterization of bipartite Gaussian states from OPO

In a recent paper by D'Auria et al (2009 Phys. Rev. Lett.102 020502) we reported the full experimental reconstruction of Gaussian entangled states generated by a type-II optical parametric oscillator (OPO) below threshold using a single homodyne detector. Here we investigate more deeply the Gaussian character of the OPO output addressing the homodyne traces. More precisely, we apply a suitable normality test to check the actual Gaussian distribution of the homodyne data and then we perform the full reconstruction of the signal.

Quantum characterization of bipartite Gaussian states

Gaussian bipartite states are basic tools for the realization of quantum information protocols with continuous variables. Their complete characterization is obtained by the reconstruction of the corresponding covariance matrix. Here we describe in details and experimentally demonstrate a robust and reliable method to fully characterize bipartite optical Gaussian states by means of a single homodyne detector. We have successfully applied our method to the bipartite states generated by a sub-threshold type-II optical parametric oscillator which produces a pair of thermal cross-polarized entangled CW frequency degenerate beams. The method provide a reliable reconstruction of the covariance matrix and allows to retrieve all the physical information about the state under investigation. These includes observable quantities, as energy and squeezing, as well as non observable ones as purity, entropy and entanglement. Our procedure also includes advanced tests for Gaussianity of the state and, overall, represents a powerful tool to study bipartite Gaussian state from the generation stage to the detection one.

Full Characterization of Gaussian Bipartite Entangled States by a Single Homodyne Detector

We present the full experimental reconstruction of Gaussian entangled states generated by a type-II optical parametric oscillator below threshold. Our scheme provides the entire covariance matrix using a single homodyne detector and allows for the complete characterization of bipartite Gaussian states, including the evaluation of purity, entanglement, and nonclassical photon correlations, without a priori assumptions on the state under investigation. Our results show that single homodyne schemes are convenient and robust setups for the full characterization of optical parametric oscillator signals and represent a tool for quantum technology based on continuous variable entanglement.

HOMODYNE CHARACTERIZATION OF CONTINUOUS VARIABLE BIPARTITE STATES

We suggest a scheme to reconstruct the covariance matrix of continuous variable two-mode states using a single homodyne detector and a few polarization elements. Our method can be used to fully characterize the bipartite Gaussian entangled states obtained at the output of a (nondegenerate) optical parametric amplifier driven below threshold, as well as to extract relevant informations on generic bipartite states made of two frequency degenerate but orthogonally polarized modes.

Adaptation de l’angiographie, au vert d’indocyanine (VIC) à la Neurochirurgie

We suggest a method to reconstruct the zero-delay-time second-order correlation function g(2)(0) of Gaussian states using a single homodyne detector. To this purpose, we have found an analytic expression of g(2)(0) for single- and two-mode Gaussian states in terms of the elements of their covariance matrix and the displacement amplitude. In the single-mode case we demonstrate our scheme experimentally, and also show that when the input state is nonclassical, there exist a threshold value of the coherent amplitude, and a range of values of the complex squeezing parameter, above which g(2)(0)<1. For amplitude squeezing and real coherent amplitude, the threshold turns out to be a necessary and sufficient condition for the nonclassicality of the state. Analogous results hold also for two-mode squeezed thermal states.

Characterization of bipartite states using a single homodyne detector

We suggest a scheme to reconstruct the covariance matrix of a two-mode state using a single homodyne detector plus a polarizing beam splitter and a polarization rotator. It can be used to fully characterize bipartite Gaussian states and to extract relevant informations on generic states.

Determination of Multimode Moments of Creation and Annihilation Operators via Multimode Balanced Homodyning with a Single Homodyne Detector

We investigate reconstruction of moments of creation and annihilation operators of multimode traveling light field from data recorded in multimode balanced homodyne detection with a single homodyne detector. We derive sampling functions whose average over the measured quadrature statistics provides the estimates of the moments. We show that detection losses may be compensated by a simple rescaling of the sampling functions. We also show that all moments of given order can be reconstructed from the statistics of a finite number of quadratures.