Showing papers by "Ping Koy Lam published in 2004"
TL;DR: A multipartite protocol to securely distribute and reconstruct a quantum state encoded into a tripartite entangled state and distributed to three players in terms of fidelity, signal transfer, and reconstruction noise is demonstrated.
Abstract: We demonstrate a multipartite protocol to securely distribute and reconstruct a quantum state. A secret quantum state is encoded into a tripartite entangled state and distributed to three players. By collaborating, any two of the three players can reconstruct the state, while individual players obtain nothing. We characterize this (2,3) threshold quantum state sharing scheme in terms of fidelity, signal transfer, and reconstruction noise. We demonstrate a fidelity averaged over all reconstruction permutations of 0.73+/-0.04, a level achievable only using quantum resources.
461 citations
TL;DR: A new coherent state quantum key distribution protocol that eliminates the need to randomly switch between measurement bases and offers the further advantage of simplicity compared to all previous protocols which, to date, have relied on switching.
Abstract: We propose a new coherent state quantum key distribution protocol that eliminates the need to randomly switch between measurement bases. This protocol provides significantly higher secret key rates with increased bandwidths than previous schemes that only make single quadrature measurements. It also offers the further advantage of simplicity compared to all previous protocols which, to date, have relied on switching.
434 citations
TL;DR: It is shown that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO.
Abstract: We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.
193 citations
TL;DR: In this paper, an experimental analysis of quadrature entanglement produced from a pair of amplitude squeezed beams is presented, and the correlation matrix of the state is characterized within a set of reasonable assumptions.
Abstract: We present an experimental analysis of quadrature entanglement produced from a pair of amplitude squeezed beams. The correlation matrix of the state is characterized within a set of reasonable assumptions, and the strength of the entanglement is gauged using measures of the degree of inseparability and the degree of Einstein-Podolsky-Rosen (EPR) paradox. We introduce controlled decoherence in the form of optical loss to the entangled state, and demonstrate qualitative differences in the response of the degrees of inseparability and EPR paradox to this loss. The entanglement is represented on a photon number diagram that provides an intuitive and physically relevant description of the state. We calculate efficacy contours for several quantum information protocols on this diagram, and use them to predict the effectiveness of our entanglement in those protocols.
93 citations
TL;DR: In this article, the authors derived the quantum noise limit for the optical beam displacement of a TEM00 mode using a multimodal analysis, and showed that the conventional split detection scheme for measuring beam displacement is non-optimal with ~80% efficiency.
Abstract: We derive the quantum noise limit for the optical beam displacement of a TEM00 mode. Using a multimodal analysis, we show that the conventional split detection scheme for measuring beam displacement is non-optimal with ~80% efficiency. We propose a new displacement measurement scheme that is optimal for small beam displacement. This scheme utilizes a homodyne detection set-up that has a TEM10 mode local oscillator. We show that although the quantum noise limit to displacement measurement can be surpassed using squeezed light in appropriate spatial modes for both schemes, the TEM10 homodyning scheme outperforms split detection for all values of squeezing.
67 citations
TL;DR: In this article, the authors derived the quantum noise limit for the optical beam displacement of a TEM00 mode using a multimodal analysis and showed that the conventional split detection scheme for measuring beam displacement is non-optimal with 80% efficiency.
Abstract: We derive the quantum noise limit for the optical beam displacement of a TEM00 mode. Using a multimodal analysis, we show that the conventional split detection scheme for measuring beam displacement is non-optimal with 80% efficiency. We propose a new displacement measurement scheme that is optimal for small beam displacement. This scheme utilises a homodyne detection setup that has a TEM10 mode local oscillator. We show that although the quantum noise limit to displacement measurement can be surpassed using squeezed light in appropriate spatial modes for both schemes, the TEM10 homodyning scheme out-performs split detection for all values of squeezing.
46 citations
TL;DR: In this paper, a lossless combination of these modes can be achieved using the non-degenerate Gouy phase shift of optical resonators, and the combined squeezed beams are measured with quadrant detectors.
Abstract: We demonstrate the possibility of surpassing the quantum noise limit for simultaneous multi-axis spatial displacement measurements that have zero mean values. The requisite resources for these measurements are squeezed light beams with exotic transverse mode profiles. We show that, in principle, lossless combination of these modes can be achieved using the non-degenerate Gouy phase shift of optical resonators. When the combined squeezed beams are measured with quadrant detectors, we experimentally demonstrate a simultaneous reduction in the transverse x- and y-displacement fluctuations of 2.2 and 3.1 dB below the quantum noise limit.
43 citations
TL;DR: In this article, a system that produces nonclassical continuous variable states of light that are squeezed at sideband frequencies below 100 kHz was demonstrated, where a single optical parametric amplifier was used in an optical noise cancellation scheme providing squeezed vacuum states with coherent bright phase modulation sidebands at higher frequencies.
22 citations
TL;DR: In this article, a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a quadrature variable modulator (QVM), is presented.
Abstract: We report on the analysis and prototype characterization of a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a quadrature variable modulator (QVM). All modulation states can be reached by tuning only the electrical inputs, facilitating real-time tuning, and the device has shown good suppression and stability properties. A mathematical analysis is presented, including the development of a geometric-phase representation for modulation. The experimental characterization of the device shows that relative suppressions of 38, 39, and 30 dB for phase, single sideband, and carrier-suppressed modulations, respectively, can be obtained as well as that the device is well behaved when scanning continuously through the parameter space of modulations. The QVM is compared with existing optical configurations that can produce amplitude and phase-modulation combinations in the context of applications such as the tuning of lock points in optical-locking schemes, single-sideband applications, modulation fast-switching applications, and applications requiring combined modulations.
17 citations
TL;DR: In this paper, the authors compare results from a bench-top experiment and a theoretical model which show how squeezed states of light may be used to modify the quantum noise behaviour of a power recycled Michelson interferometer.
Abstract: The sensitivity of interferometric gravitational wave detectors is ultimately limited by the 'quantum noise' of light In this paper we compare results from a bench-top experiment and a theoretical model which show how squeezed states of light may be used to modify the quantum noise behaviour of a power recycled Michelson interferometer We develop a simple theoretical model of the experiment and find close agreement of theoretical and experimental results We measure quantum noise suppression of 23 dB and demonstrate the lock stability of the experiment for long periods
8 citations
25 May 2004
TL;DR: A multipartite protocol that utilizes entanglement to securely distribute and reconstruct a quantum state and a fidelity averaged over all reconstruction permutations of 0.73 ± 0.04, a level achievable only using quantum resources.
Abstract: We demonstrate a multipartite protocol that utilizes entanglement to securely distribute and reconstruct aquantum state. A secret quantum state is encoded into a tripartite entangled state and distributed to threeplayers. By collaborating together, a majority of the players can reconstruct the state, whilst the remainingplayer obtains nothing. This (2 ,3) threshold quantum state sharing scheme is characterized in terms of Þdelity(F ), signal transfer ( T ) and reconstruction noise ( V ). We demonstrate a Þdelity averaged over all reconstructionpermutations of 0 .73 ± 0.04, a level achievable only using quantum resources.Keywords: quantum information, quantum network, quantum state sharing, quantum cryptography, quantumsecret sharing, entanglement, optical parametric ampliÞer 1. INTRODUCTION In conventional cryptography, secret sharing is a powerful technique which enables a dealer to securely distributeinformation to multiple players (the recipients) who are not all necessarily trustworthy. Secret sharing techniqueshave many present-day applications involving the management of cryptographic keys in information networkssuch as the internet, telecommunication systems and distributed computers. An important class of secret sharingprotocols is ( k,n ) threshold secret sharing,
01 Jan 2004
TL;DR: The toxicity of 5-chlorouracil (as measured by DNA strand breakage) was significantly influenced by time from dosing and there was no significant difference in MML between mice dosed with 5- chloro-6-hydroxymethyluracil and the controls.
Abstract: Cylindrospermopsin (CYN), a potent cyanobacterial hepatotoxin produced by Cylindrospermopsis raciborskii and other cyanobacteria, is regularly found in water supplies in many parts of the world and has been associated with the intoxication of humans and livestock.Water treatment via chlorination can degrade the toxin effectively but result in the production of several byproducts. In this study, male and female Balb/c mice were injected via the intraperitoneal (IP) route with a single dose of 10 mg/kg 5-chlorouracil and 10 mg/kg 5-chloro-6-hydroxymethyluracil; these two compounds are the predicted chlorinated degradation products of CYN.DNA was isolated from the mouse livers and examined for strand breakage by alkaline gel electrophoresis (pH 12). The median molecular length (MML) of the DNA distributed in the gel was determined by estimating the midpoint of the DNA size distribution by densitometry. The toxicity of 5-chlorouracil (as measured by DNA strand breakage) was significantly influenced by time from dosing. There was no significant difference in MML between mice dosed with 5-chloro-6-hydroxymethyluracil and the controls. In another experiment, mice were dosed with 0, 0.1, 1, 10 and 100 mg/kg body weight 5-chlorouracil and 0, 0.1, 1, 10 and 20 mg/kg 5-chloro-6-hydroxymethyluracil via IP injection. The heart, liver, kidney, lung and spleen were removed, fixed and examined under electron microscopy. Liver was the main target organ. The EM results revealed marked distortion on the nuclear membrane of liver cells in mice dosed with 1.0 mg/kg 5-chlorouracil or 10 mg/kg 5-chloro-6-hydroxymethyluracil, or higher.
03 Feb 2004
TL;DR: In this paper, the authors present a survey of the state-of-the-art solutions for the problem of cyber bullying in the context of cyber-physical bullying and cyber-bullying.
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