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Search Results: 1 - 10 of 225567 matches for " Timothy C. Ralph "
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Transfer of Nonclassical Properties from A Microscopic Superposition to Macroscopic Thermal States in The High Temperature Limit
Hyunseok Jeong,Timothy C. Ralph
Physics , 2004, DOI: 10.1103/PhysRevLett.97.100401
Abstract: We present several examples where prominent quantum properties are transferred from a microscopic superposition to thermal states at high temperatures. Our work is motivated by an analogy of Schrodinger's cat paradox, where the state corresponding to the virtual cat is a mixed thermal state with a large average photon number. Remarkably, quantum entanglement can be produced between thermal states with nearly the maximum Bell-inequality violation even when the temperatures of both modes approach infinity.
Quantum superpositions and entanglement of thermal states at high temperatures and their applications to quantum information processing
Hyunseok Jeong,Timothy C. Ralph
Physics , 2007, DOI: 10.1103/PhysRevA.76.042103
Abstract: We study characteristics of superpositions and entanglement of thermal states at high temperatures and discuss their applications to quantum information processing. We introduce thermal-state qubits and thermal-Bell states, which are a generalization of pure-state qubits and Bell states to thermal mixtures. A scheme is then presented to discriminate between the four thermal-Bell states without photon number resolving detection but with Kerr nonlinear interactions and two single-photon detectors. This enables one to perform quantum teleportation and gate operations for quantum computation with thermal-state qubits.
Entanglement between the future and past in the quantum vacuum
S. Jay Olson,Timothy C. Ralph
Physics , 2010, DOI: 10.1103/PhysRevLett.106.110404
Abstract: We note that massless fields within the future and past light cone may be quantized as independent systems. We show that the vacuum is an entangled state of these systems, exactly mirroring the known entanglement between the spacelike separated Rindler wedges. We describe a detector which exhibits a thermal response to the vacuum when switched on at t=0. The feasibility of experimentally detecting this effect is discussed.
Error models for mode-mismatch in linear optics quantum computing
Peter P. Rohde,Timothy C. Ralph
Physics , 2006, DOI: 10.1103/PhysRevA.73.062312
Abstract: One of the most significant challenges facing the development of linear optics quantum computing (LOQC) is mode-mismatch, whereby photon distinguishability is introduced within circuits, undermining quantum interference effects. We examine the effects of mode-mismatch on the parity (or fusion) gate, the fundamental building block in several recent LOQC schemes. We derive simple error models for the effects of mode-mismatch on its operation, and relate these error models to current fault tolerant threshold estimates.
Optical Zeno Gate: Bounds for Fault Tolerant Operation
Patrick M. Leung,Timothy C. Ralph
Physics , 2007, DOI: 10.1088/1367-2630/9/7/224
Abstract: In principle the Zeno effect controlled-sign gate of Franson et al's (PRA 70, 062302, 2004) is a deterministic two-qubit optical gate. However, when realistic values of photon loss are considered its fidelity is significantly reduced. Here we consider the use of measurement based quantum processing techniques to enhance the operation of the Zeno gate. With the help of quantum teleportation, we show that it is possible to achieve a Zeno CNOT gate (GC-Zeno gate) that gives (near) unit fidelity and moderate probability of success of 0.76 with a one-photon to two-photon transmission ratio $\kappa=10^4$. We include some mode-mismatch effects and estimate the bounds on the mode overlap and $\kappa$ for which fault tolerant operation would be possible.
Frequency and temporal effects in linear optical quantum computing
Peter P. Rohde,Timothy C. Ralph
Physics , 2004, DOI: 10.1103/PhysRevA.71.032320
Abstract: Typically linear optical quantum computing (LOQC) models assume that all input photons are completely indistinguishable. In practice there will inevitably be non-idealities associated with the photons and the experimental setup which will introduce a degree of distinguishability between photons. We consider a non-deterministic optical controlled-NOT gate, a fundamental LOQC gate, and examine the effect of temporal and spectral distinguishability on its operation. We also consider the effect of utilizing non-ideal photon counters, which have finite bandwidth and time response.
Modeling photo-detectors in quantum optics
Peter P. Rohde,Timothy C. Ralph
Physics , 2005, DOI: 10.1080/09500340600578369
Abstract: Photo-detection plays a fundamental role in experimental quantum optics and is of particular importance in the emerging field of linear optics quantum computing. Present theoretical treatment of photo-detectors is highly idealized and fails to consider many important physical effects. We present a physically motivated model for photo-detectors which accommodates for the effects of finite resolution, bandwidth and efficiency, as well as dark-counts and dead-time. We apply our model to two simple well known applications, which illustrates the significance of these characteristics.
Arbitrarily Large Continuous-Variable Cluster States from a Single Quantum Nondemolition Gate
Nicolas C. Menicucci,Xian Ma,Timothy C. Ralph
Physics , 2010, DOI: 10.1103/PhysRevLett.104.250503
Abstract: We present a compact experimental design for producing an arbitrarily large optical continuous-variable cluster state using just one single-mode vacuum squeezer and one quantum nondemolition gate. Generating the cluster state and computing with it happen simultaneously: more entangled modes become available as previous modes are measured, thereby making finite the requirements for coherence and stability even as the computation length increases indefinitely.
Noiseless phase quadrature amplification via electro-optic feed-forward
Ben C. Buchler,Elanor H. Huntington,Timothy C. Ralph
Physics , 1998, DOI: 10.1103/PhysRevA.60.529
Abstract: Theoretical results are presented which show that noiseless phase quadrature amplification is possible, and limited experimentally only by the efficiency of the phase detection system. Experimental results obtained using a Nd:YAG laser show a signal gain of 10dB and a signal transfer ratio of T_s=0.9. This result easily exceeds the standard quantum limit for signal transfer. The results also explicitly demonstrate the phase sensitive nature of the amplification process.
Quantum Cryptography Approaching the Classical Limit
Christian Weedbrook,Stefano Pirandola,Seth Lloyd,Timothy C. Ralph
Physics , 2010, DOI: 10.1103/PhysRevLett.105.110501
Abstract: We consider the security of continuous-variable quantum cryptography as we approach the classical-limit, i.e., when the unknown preparation noise at the sender's station becomes significantly noisy or thermal (even by as much as 10,000 times the variance of the vacuum mode). We show that, provided the channel transmission losses do not exceed 50%, the security of quantum cryptography is not dependent on the channel transmission, and is therefore, incredibly robust against significant amounts of excess preparation noise. We extend these results to consider for the first time quantum cryptography at wavelengths considerably longer than optical and find that regions of security still exist all the way down to the microwave.
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