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QUANTUM CORRELATIONS OF LIGHTS IN MACROSCOPIC ENVIRONMENTS

Yong Meng Sua

Published Jan 1, 2014• 0 citations
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Abstract

This dissertation presents a detailed study in exploring quantum correlations of lights in macroscopic environments. We have explored quantum correlations of single photons, weak coherent states, and polarization-correlated/polarization-entangled photons in macroscopic environments. These included macroscopic mirrors, macroscopic photon number, spatially separated observers, noisy photons source and propagation medium with loss or disturbances. We proposed a measurement scheme for observing quantum correlations and entanglement in the spatial properties of two macroscopic mirrors using single photons spatial compass state. We explored the phase space distribution features of spatial compass states, such as chessboard pattern by using the Wigner function. The displacement and tilt correlations of the two mirrors were manifested through the propensities of the compass states. This technique can be used to extract Einstein-Podolsky-Rosen correlations (EPR) of the two mirrors. We then formulated the discrete-like property of the propensity Pb(m,n), which can be used to explore environmental perturbed quantum jumps of the EPR correlations in phase space. With single photons spatial compass state, the variances in position and momentum are much smaller than standard quantum limit when using a Gaussian TEM00 beam. We observed intrinsic quantum correlations of weak coherent states between two parties through balanced homodyne detection. Our scheme can be used as a supplement to decoy-state BB84 protocol and differential phase-shift QKD protocol. We prepared four types of bipartite correlations ±cos2(θ12) that shared between two parties. We also demonstrated bits correlations between two parties separated by 10 km optical fiber. The bits information will be protected by the large quantum phase fluctuation of weak coherent states, adding another physical layer of security to these protocols for quantum key distribution. Using 10 m of highly nonlinear fiber (HNLF) at 77 K, we observed coincidence to accidental-coincidence ratio of 130±5 for correlated photon-pair and Two-Photon Interference visibility >98% entangled photon-pair. We also verified the non-local behavior of polarization-entangled photon pair by violating Clauser-Horne-Shimony-Holt Bell’s inequality by more than 12 standard deviations. With the HNLF at 300 K (77 K), photon-pair production rate about factor 3(2) higher than a 300 m dispersion-shifted fiber is observed. Then, we studied quantum correlation and interference of photon-pairs; with one photon of the photon-air experiencing multiple scattering in a random medium. We observed that depolarization noise photon in multiple scattering degrading the purity of photon-pair, and the existence of Raman noise photon in a photon-pair source will contribute to the depolarization affect. We found that quantum

DOI
10.37099/mtu.dc.etds/769

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This dissertation presents a detailed study in exploring quantum correlations of lights in macroscopic environments. We have explored quantum correlations of single photons, weak coherent states, and polarization-correlated/polarization-entangled photons in macroscopic environments. These included macroscopic mirrors, macroscopic photon number, spatially separated observers, noisy photons source and propagation medium with loss or disturbances. We proposed a measurement scheme for observing quantum correlations and entanglement in the spatial properties of two macroscopic mirrors using single photons spatial compass state. We explored the phase space distribution features of spatial compass states, such as chessboard pattern by using the Wigner function. The displacement and tilt correlations of the two mirrors were manifested through the propensities of the compass states. This technique can be used to extract Einstein-Podolsky-Rosen correlations (EPR) of the two mirrors. We then formulated the discrete-like property of the propensity Pb(m,n), which can be used to explore environmental perturbed quantum jumps of the EPR correlations in phase space. With single photons spatial compass state, the variances in position and momentum are much smaller than standard quantum limit when using a Gaussian TEM00 beam. We observed intrinsic quantum correlations of weak coherent states between two parties through balanced homodyne detection. Our scheme can be used as a supplement to decoy-state BB84 protocol and differential phase-shift QKD protocol. We prepared four types of bipartite correlations ±cos2(θ12) that shared between two parties. We also demonstrated bits correlations between two parties separated by 10 km optical fiber. The bits information will be protected by the large quantum phase fluctuation of weak coherent states, adding another physical layer of security to these protocols for quantum key distribution. Using 10 m of highly nonlinear fiber (HNLF) at 77 K, we observed coincidence to accidental-coincidence ratio of 130±5 for correlated photon-pair and Two-Photon Interference visibility >98% entangled photon-pair. We also verified the non-local behavior of polarization-entangled photon pair by violating Clauser-Horne-Shimony-Holt Bell’s inequality by more than 12 standard deviations. With the HNLF at 300 K (77 K), photon-pair production rate about factor 3(2) higher than a 300 m dispersion-shifted fiber is observed. Then, we studied quantum correlation and interference of photon-pairs; with one photon of the photon-air experiencing multiple scattering in a random medium. We observed that depolarization noise photon in multiple scattering degrading the purity of photon-pair, and the existence of Raman noise photon in a photon-pair source will contribute to the depolarization affect. We found that quantum
Intrinsic quantum correlations of weak coherent states are observed between two parties through a novel detection scheme, which can be used as a supplement to the existence decoy-state BB84 and differential phase-shift quantum key distribution (DPS-QKD) protocols. In a proof-of-principle experiment, we generate bi-partite correlations of weak coherent states using weak local oscillator fields in two spatially separated balanced homodyne detections. We employ nonlinearity of post-measurement method to obtain the bi-partite correlations from two single-field interferences at individual homodyne measurement. This scheme is then used to demonstrate bits correlations between two parties over a distance of 10 km through a transmission fiber. We believe that the scheme can add another physical layer of security to these protocols for quantum key distribution.
Intrinsic quantum correlations of weak coherent states are observed between two parties through a novel detection scheme, which can be used as a supplement to the existence decoy-state Bennett-Brassard 1984 protocol and the differential phase-shift quantum key distribution (DPS-QKD) protocol. In a proof-of-principle experiment, we generate bipartite correlations of weak coherent states using weak local oscillator fields in two spatially separated balanced homodyne detections. We employ a nonlinearity of postmeasurement method to obtain the bipartite correlations from two single-field interferences at individual homodyne measurements. This scheme is then used to demonstrate bits correlations between two parties over a distance of 10 km through a transmission fiber. We believe that the scheme can add another physical layer of security to these protocols for quantum key distribution.
Quantum information science explores the foundational aspects of quantum mechanics and its ombination with information science for new information technologies. The underlying key resource is non-classical correlations. These counter-intuitive correlations between quantum systems can be used for encoding, transmitting and measuring information in quantum information tasks. Although quantum properties can be used in a variety of systems, here we explore photons. These information carriers are fast, easy to generate and manipulate and only interact weakly with the environment. These properties make them to excellent candidates to be employed in experiments. Developing quantum technology, such as single photon sources and single photon detectors, allows us to investigate the foundational aspects of quantum mechanics in quantum information tasks. These tasks use non-classical correlations, which form a hierarchy, from Bell nonlocality to Einstein-Podolsky-Rosen (EPR) steering to quantum nonseparability. Two systems are nonlocally correlated, when measuring one system affects the measurement results on the other system, hence the name `steering. In test for non-classical correlations, we share a quantum state between two observers which are trusted or untrusted. While observers are both untrusted or trusted in entanglement witness tests and Bell inequality violations, respectively, EPR-steering is distinct from these two classes by its fundamental asymmetry: one party is trusted while the other is untrusted.
We propose a measurement scheme for observing quantum correlations and entanglement in the spatial properties of two macroscopic mirrors. Two spatial versions of compass states are generated by using a single Gaussian mode of single photons in a simple interferometer. The chessboard pattern of spatial compass states reflects the spatial properties of a mirror composed of NNN quantum mirrors. The displacement and tilt correlations of the two mirrors are manifested by single photons and projection measurements through a measuring device which measures the propensities of the compass states. The technique can extract mechanical correlations of the two mirrors and lock them into the Einstein-Podolsky-Rosen (EPR) correlation. The criteria for EPR entanglement of these mirrors are then verified by sub-Planck structures in the propensity. We formulate the discrete-like property of the propensity, a demonstration of quantum jumps of EPR correlations in phase space, which, hence, enables discrete phase-space quantum computing and information processing.
One of the most intriguing concepts of quantum mechanics is quantum entanglement. Two physical systems are said to be entangled with respect to a certain variable, if their individual outcomes of the variable are undetermined before measurement, but strictly correlated. Measurement of the variable for only one system immediately determines the outcome for the other system, irrespective of the distance between the two systems. It is this strong correlation that provides a basis for perspective, powerful applications like quantum cryptography and quantum computation. The most studied entangled systems, often called EPR systems (after the pioneers Einstein, Podolsky and Rosen), are pairs of light particles or photon pairs. These photon pairs, usually generated via the optical process of a spontaneous parametric down-conversion, are, in principal, simultaneously entangled in three variables, being polarization (polarization entanglement), energy or time (time entanglement), and momentum or transverse space (spatial entanglement). The contents of this thesis cover new insights in the polarization and spatial entanglement of photons. We have investigated both the entanglement quality and the yield of entangled photons for different experimental geometries that are associated with the production and detection of the photons.
In this work we focus our attention on the correlation properties of a new class of bright nonclassical states of light, which are called the macroscopic Bell states [1,2]. These states are of interest in quantum optics due to their rarely combined two properties: brightness and quantumness. Recently we have investigated the polarization properties of these states, namely we have shown that the macroscopic singlet state is absolutely unpolarized and free of polarization noise [2], while the triplet states reveal the effect of hidden polarization [3]. Now we experimentally prove that both singlet and triplet macroscopic Bell states are entangled.