Showing papers by "Ping Koy Lam published in 2013"
TL;DR: In this article, the authors inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz.
Abstract: Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earth-based gravitational wave observatories1, 2, 3, 4 is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometre-level sensitivity of the kilometre-scale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitational-wave Universe with unprecedented sensitivity.
805 citations
TL;DR: In this paper, a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection" where the signal was not initially revealed to the collaboration.
Abstract: Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational-wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance, that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection'' where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron-star and black-hole binary parameter space over the component mass range 1M(circle dot)-25M(circle dot) and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.
136 citations
TL;DR: In this article, the authors reported a search for gravitational waves from the inspiral, merger and ringdown of binary black holes with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010.
Abstract: We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20, 20)M-circle dot coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28M(circle dot) of 3:3 x 10(-7) mergers Mpc(-3) yr(-1).
108 citations
TL;DR: In this paper, the results of an all-sky search for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative range of similar to [-20, 1.1] x 10(-10) Hz s(-1) for the fifth LIGO science run (S5) are presented.
Abstract: This paper presents results of an all-sky search for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative range of similar to[-20, 1.1] x 10(-10) Hz s(-1) for the fifth LIGO science run (S5). The search uses a noncoherent Hough-transform method to combine the information from coherent searches on time scales of about one day. Because these searches are very computationally intensive, they have been carried out with the Einstein@Home volunteer distributed computing project. Postprocessing identifies eight candidate signals; deeper follow-up studies rule them out. Hence, since no gravitational wave signals have been found, we report upper limits on the intrinsic gravitational wave strain amplitude h(0). For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h(0) greater than 7.6 x 10(-25) at a 90% confidence level. This search is about a factor 3 more sensitive than the previous Einstein@Home search of early S5 LIGO data.
100 citations
Journal Article•
89 citations
12 May 2013
TL;DR: In this paper, an ensemble of cold Cesium atoms trapped in a MOT, interacting with light via a Λ-type scheme on the D2 line, were analyzed for various values of the control Rabi frequency Ω between 0.1Γ and 4Γ, where Γ is the natural linewidth.
Abstract: Summary form only given. If in general the transparency of an initially absorbing medium for a probe field is increased by the presence of a control field on an adjacent transition, two very different processes can be invoked to explain it. One of them is a quantum Fano interference between two paths in the three-level system, which occurs even at low control intensity and gives rise to electromagnetically-induced transparency (EIT), the other one is the appearance of two dressed states in the excited level at higher control intensity, corresponding to the Autler-Townes splitting (ATS). This distinction is particularly critical for instance for the implementation of slow light or optical quantum memories. In a recent paper, P. M. Anisimov, J. P. Dowling and B. C. Sanders proposed a quantitative test to objectively discerning ATS from EIT. We experimentally investigated this test with cold atoms and demonstrated that it is very sensitive to the specific properties of the medium. In this study, we use an ensemble of cold Cesium atoms trapped in a MOT, interacting with light via a Λ-type scheme on the D2 line. Absorption profiles are obtained for various values of the control Rabi frequency Ω between 0.1Γ and 4Γ, where Γ is the natural linewidth.
84 citations
TL;DR: It is shown that the postselection protocol is equivalent to a virtual entanglement-based protocol including a distillation stage and a particular ‘Gaussian’ post selection is introduced and it is demonstrated that the security can be calculated using only experimentally accessible quantities.
Abstract: We extend the security analysis of continuous variable quantum-key-distribution protocols using a family of post selection schemes to account for arbitrary eavesdropping attacks. We show that the postselection protocol is equivalent to a virtual entanglement-based protocol including a distillation stage. We introduce a particular ‘Gaussian’ post selection and demonstrate that the security can be calculated using only experimentally accessible quantities. Finally, we explicitly evaluate the performance for the case of a noisy Gaussian channel in the limit of unbounded key length and find improvements over all pre-existing continuous variable protocols in realistic regimes.
72 citations
TL;DR: Calculations of several effects that lead to quadrature fluctuations are presented, and estimates are used to account for the observed quadratures fluctuations in a LIGO gravitational wave detector.
Abstract: Squeezed states of light are an important tool for optical measurements below the shot noise limit and for optical realizations of quantum information systems. Recently, squeezed vacuum states were deployed to enhance the shot noise limited performance of gravitational wave detectors. In most practical implementations of squeezing enhancement, relative fluctuations between the squeezed quadrature angle and the measured quadrature (sometimes called squeezing angle jitter or phase noise) are one limit to the noise reduction that can be achieved. We present calculations of several effects that lead to quadrature fluctuations, and use these estimates to account for the observed quadrature fluctuations in a LIGO gravitational wave detector. We discuss the implications of this work for quantum enhanced advanced detectors and even more sensitive third generation detectors.
72 citations
TL;DR: In this paper, a magneto-optical trap with a peak optical depth of 1000 for the D2 F = 2! F 0 = 3 transition using spatial and temporal dark spots is presented.
Abstract: Quantum memories are an integral component of quantum repeaters—devices that will allow the extension of quantum key distribution to communication ranges beyond that permissible by passive transmission. A quantum memory for this application needs to be highly efficient and have coherence times approaching a millisecond. Here we report on work towards this goal, with the development of a 87 Rb magneto-optical trap with a peak optical depth of 1000 for the D2 F = 2 ! F 0 = 3 transition using spatial and temporal dark spots. With this purpose-built cold atomic ensemble we implemented the gradient echo memory (GEM) scheme on the D1 line. Our data shows a memory efficiency of 80±2% and coherence times up to 195µs, which is a factor of four greater than previous GEM experiments implemented in warm vapour cells.
68 citations
TL;DR: In this paper, the authors report on the generation of optical vortex beams using spatial phase modulation with spiral phase mirrors, and they directly observed the successful generation of an optical vortex beam with a charge as high as 5050.
Abstract: We report on the generation of optical vortex beams using spatial phase modulation with spiral phase mirrors. The spiral phase mirrors are manufactured by direct machining with an ultra-precision single point diamond turning lathe. The imperfection of the machined phase mirrors and its impact on the generated vortex beams are analyzed with interferometric measurements. Our phase mirror has a surface roughness of 3 nm and a maximum peak–valley deviation of λ/30. The vortex charges of our light beams are directly verified by counting the fringes of their corresponding interferograms. We directly observed the successful generation of an optical vortex beam with a charge as high as 5050. We study the Fourier images of the vortex beams to characterize the quality of the beams. We obtained a conversion efficiency of 92.8% from a TEM00 beam to a vortex beam with charge 1020. This technique of generating optical singularities can potentially be used to produce more complex optical wavefronts, such as optical knots.
58 citations
TL;DR: In this article, the results of the first search for gravitational wave bursts associated with high energy neutrinos were presented, which could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy.
Abstract: We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.
TL;DR: The proposed scheme is an extreme example of the optical spring, where a mechanical oscillator is isolated from the environment and its mechanical frequency and macroscopic state can be manipulated solely through optical fields.
Abstract: We demonstrate the feasibility of levitating a small mirror using only radiation pressure In our scheme, the mirror is supported by a tripod where each leg of the tripod is a Fabry-Perot cavity The macroscopic state of the mirror is coherently coupled to the supporting cavity modes allowing coherent interrogation and manipulation of the mirror motion The proposed scheme is an extreme example of the optical spring, where a mechanical oscillator is isolated from the environment and its mechanical frequency and macroscopic state can be manipulated solely through optical fields We model the stability of the system and find a three-dimensional lattice of trapping points where cavity resonances allow for buildup of optical field sufficient to support the weight of the mirror Our scheme offers a unique platform for studying quantum and classical optomechanics and can potentially be used for precision gravitational field sensing and quantum state generation
TL;DR: It has now been shown that long-distance cryptographic communication is just as effective when the scheme involves measuring the wave properties of light, rather than its particle properties.
Abstract: Using photons to disseminate encryption codes with complete security is one of the great successes of quantum information science. It has now been shown that long-distance cryptographic communication is just as effective when the scheme involves measuring the wave properties of light, rather than its particle properties.
TL;DR: In this paper, the authors present a direct measurement of the impact of backscattered light from a squeezed light source deployed on one of the 4 km long detectors of the Laser Interferometric Gravitational Wave Observatory (LIGO).
Abstract: Squeezed states of light have been recently used to improve the sensitivity of laser interferometric gravitational-wave detectors beyond the quantum limit. To completely establish quantum engineering as a realistic option for the next generation of detectors, it is crucial to study and quantify the noise coupling mechanisms which injection of squeezed states could potentially introduce. We present a direct measurement of the impact of backscattered light from a squeezed-light source deployed on one of the 4 km long detectors of the Laser Interferometric Gravitational Wave Observatory (LIGO). We also show how our measurements inform the design of squeezed light sources compatible with the even more sensitive advanced detectors currently under construction, such as Advanced LIGO.
TL;DR: In this paper, phase randomized homodyne measurements were used to reconstruct the Wigner functions of a photon number conditioned state from a photon subtracted squeezed vacuum state, without using a photon counting detector.
Abstract: We experimentally demonstrate the reconstruction of a photon number conditioned state without using a photon number discriminating detector. By using only phase randomized homodyne measurements, we reconstruct up to the three photon subtracted squeezed vacuum state. The reconstructed Wigner functions of these states show regions of pronounced negativity, signifying the non-classical nature of the reconstructed states. The techniques presented allow for complete characterization of the role of a conditional measurement on an ensemble of states, and might prove useful in systems where photon counting still proves technically challenging.
06 Dec 2013
TL;DR: In this article, a magneto-optical trap with a peak optical depth of 1000 for the D2 F = 2? F' = 3 transition using spatial and temporal dark spots is presented.
Abstract: Quantum memories for light lie at the heart of long-distance provably-secure communication. Demand for a functioning quantum memory, with high efficiency and coherence times approaching a millisecond, is therefore at a premium. Here we report on work towards this goal, with the development of a 87Rb magneto-optical trap with a peak optical depth of 1000 for the D2 F = 2 ? F' = 3 transition using spatial and temporal dark spots. With this purpose-built cold atomic ensemble we implemented the gradient echo memory (GEM) scheme on the D1 line. Our data shows a memory efficiency of 80 ? 2% and coherence times up to 195 ?s.
TL;DR: A secure communication channel that relies on quantum entanglement survives despite the noisy break up of theEntanglement itself.
Abstract: A secure communication channel that relies on quantum entanglement survives despite the noisy break up of the entanglement itself.
TL;DR: The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient that leads to rephasing of the atomic polarization and thus recall of the stored optical state.
Abstract: Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.
TL;DR: In this article, the authors proposed using quantum memory to map optical fields into Fourier transformed polaritonic excitations in an atomic ensemble and showed that nonlinear optical interactions can be induced during the storage process.
Abstract: We present a proposal for using quantum memory to map optical fields into Fourier transformed polaritonic excitations in an atomic ensemble. We show that nonlinear optical interactions can be induced during the storage process.
TL;DR: In this article, a photon echo scheme that works with warm and cold atomic ensembles is used to perform quantum memory with high efficiency and the ability to manipulate the stored light while it is stored.
Abstract: Our quantum memory uses a photon echo scheme that works with warm and cold atomic ensembles. We show high efficiency (up to 87%) and the ability to manipulate the stored light while it is stored.
12 May 2013
TL;DR: In this paper, it was shown that a non-classical quantity called quantum discord is all that is required to perform efficient quantum computation and that quantum entanglement is not necessary.
Abstract: For many years, the notion of quantum correlations was equated with the notion of quantum entanglement. The wide range of quantum protocols whose extra-powers over classical protocol were shown to originate from quantum entanglement mostly motivated this. For example, it was shown that for certain class of problems, a quantum computer could provide exponential speed-up over its classical counterpart, given that it relied on quantum entangled resources. Recently, however, the requirement of possessing entanglement to perform efficient quantum computation has been questioned both theoretically [1] and experimentally [2]. It appears that a non-classical quantity called quantum discord [3] is all that is required.
Journal Article•
TL;DR: A secure communication channel that relies on quantum entanglement survives despite the noisy break up of theEntanglement itself.
Abstract: A secure communication channel that relies on quantum entanglement survives despite the noisy break up of the entanglement itself
30 Jun 2013
TL;DR: In this article, it was shown that quantum processors can harness discord to perform tasks classical counterparts cannot, via experimental Gaussian optics, and that discord is a more general quantum resource than entanglement.
Abstract: Quantum discord is conjectured to be a more general quantum resource than entanglement. We support this conjecture by showing, via experimental Gaussian optics, that quantum processors can harness discord to perform tasks classical counterparts cannot.
12 May 2013
TL;DR: Continuous Variable (CV) Quantum Key Distribution has the advantage of high raw bit rates due to the high efficiency and high bandwidth of homodyne detection and ease of integration with existing communications infrastructure.
Abstract: Continuous Variable (CV) Quantum Key Distribution (QKD) has the advantage of high raw bit rates due to the high efficiency and high bandwidth of homodyne detection and ease of integration with existing communications infrastructure. CV protocols that employ Post-Selection (PS) [1] - a classical filtering of the measurement results - enjoy additional advantages in terms of versatility and reconciliation efficiency.
30 Jun 2013
TL;DR: A quantum repeater scheme that uses gradient echo memory and probabilistic noiseless amplification and shows that a quantum memory can process quantum information and aNoiseless amplifier can distill entanglement is presented.
Abstract: We present a quantum repeater scheme that uses gradient echo memory and probabilistic noiseless amplification. We show that a quantum memory can process quantum information and a noiseless amplifier can distill entanglement.
08 Jul 2013
TL;DR: By using a carefully tailored post-selection protocol, this work proves unconditional security and shows that significant performance improvements are achieved.
Abstract: Post-selection is a standard part of discrete variable QKD protocols, however attempts to prove security when post-selection is deployed in continuous variable QKD protocols have until now been limited. Here, by using a carefully tailored post-selection protocol, we prove unconditional security and show that significant performance improvements are achieved.
12 May 2013
TL;DR: This experiment presents an experiment that taps to the Heisenberg uncertainty relation to provide a fast and reliable stream of random bits and ensures that the randomness in the final bits is solely driven by the quantum fluctuations.
Abstract: The availability of fast and good quality random numbers is necessary to deploy quantum key distribution devices. The state of the universe according to classical mechanics is perfectly determined via its initial conditions. However, in quantum mechanics, the Heisenberg uncertainty relation provides a source of randomness. We present an experiment that taps to this source to provide a fast and reliable stream of random bits.
09 Jun 2013
TL;DR: In this paper, the authors investigated a method that allows for objectively discerning between the Autler-Townes splitting and the electromagnetically-induced transparency models, and demonstrated the suitability of the test and additionally showed its sensitivity to the medium properties.
Abstract: We investigated a method that allows for objectively discerning between the Autler-Townes splitting and the electromagnetically-induced transparency models. We demonstrated the suitability of the test and additionally show its sensitivity to the medium properties.
TL;DR: In this paper, the authors introduce a simple and efficient technique to verify quantum discord in unknown Gaussian states and a certain class of non-Gaussian states, where any separation in the peaks of the marginal distributions of one subsystem conditioned on two different outcomes of homodyne measurements performed on the other subsystem indicates correlation between the corresponding quadratures, and hence nonzero discord.
Abstract: We introduce a simple and efficient technique to verify quantum discord in unknown Gaussian states and a certain class of non-Gaussian states. We show that any separation in the peaks of the marginal distributions of one subsystem conditioned on two different outcomes of homodyne measurements performed on the other subsystem indicates correlation between the corresponding quadratures, and hence nonzero discord. We also apply this method to non-Gaussian states that are prepared by overlapping a statistical mixture of coherent and vacuum states on a beam splitter. We experimentally demonstrate this technique by verifying nonzero quantum discord in a bipartite Gaussian and certain class of non-Gaussian states.