Quantum Computing with Continuous-Variable Clusters (2009)
Gu, Mile, Weedbrook, Christian, Menicucci, Nicolas C., Ralph, Timothy C., Van Loock, Peter
Continuous-variable cluster states offer a potentially promising method of implementing a quantum computer. This paper extends and further refines theoretical foundations and protocols for...
Distinguishability of Gaussian States in Quantum Cryptography using Post-Selection (2009)
Weedbrook, Christian, Alton, Daniel J., Symul, Thomas, Lam, Ping Koy, Ralph, Timothy C.
We consider the distinguishability of Gaussian states from the view point of continuous-variable quantum cryptography using post-selection. Specifically, we use the probability of error to...
Methods for linear optical quantum Fredkin gate (2008)
Gong, Yan-Xiao, Guo, Guang-Can, Ralph, Timothy C.
We consider the realization of quantum Fredkin gate with only linear optics and single photons. First we construct a heralded Fredkin gate using four heralded controlled-not (CNOT) gates. Then we...
Experimental demonstration of an all-optical CNOT gate (2008)
Timothy C. Ralph, David Branning
Abstract. We report the first unambiguous experimental demonstration and comprehensive characterisation of quantum CNOT operation: producing all four entangled Bell states with high fidelity as a...
Methods for a linear optical quantum Fredkin gate (2008)
Gong, Yan-Xiao, Guo, Guang-Can, Ralph, Timothy C.
We consider the realization of a quantum Fredkin gate with only linear optics and single photons. First we construct a heralded Fredkin gate using four heralded controlled-NOT (CNOT) gates. Then we...
Practical effects in the preparation of cluster states using weak non-linearities (2008)
Rohde, Peter P., Munro, William J., Ralph, Timothy C., Van Loock, Peter, Nemoto, Kae
We discuss experimental effects in the implementation of a recent scheme for performing bus mediated entangling operations between qubits. Here a bus mode, a strong coherent state, successively...
The CHSH-bell inequality and Tsirelson's bound with postselection (2008)
Berry, Dominic W, Hyunseok, Jeong, Stobinska, Magdalena, Ralph, Timothy C.
We show the necessary and sufficient conditions on loss for valid CHSH-Bell experiments, and propose an experiment with loss which should violate Tsirelsonpsilas bound for entangled states.
The CHSH-Bell inequality and Tsirelson's bound with postselection (2007)
Berry, Dominic W., Jeong, Hyunseok, Stobinska, Magdalena, Ralph, Timothy C.
We find the necessary and sufficient condition on postselection for the CHSH-Bell inequality to hold for local realistic theories. This condition is weaker than the usual fair sampling assumption,...
Quantum Cloning of Continuous Variable Entangled States (2007)
Weedbrook, Christian, Grosse, Nicolai B., Symul, Thomas, Lam, Ping Koy, Ralph, Timothy C.
We consider the quantum cloning of continuous variable entangled states. This is achieved by introducing two symmetric entanglement cloning machines (or e-cloners): a local e-cloner and a global...
Practical effects in the preparation of cluster states using weak non-linearities (2007)
Rohde, Peter P., Munro, William J., Ralph, Timothy C., Van Loock, Peter, Nemoto, Kae
We discuss experimental effects in the implementation of a recent scheme for performing bus mediated entangling operations between qubits. Here a bus mode, a strong coherent state, successively...
Rohde, Peter P., Webb, James G., Huntington, Elanor H., Ralph, Timothy C.
Number-resolving photo-detection is necessary for many quantum optics experiments, especially in the application of entangled state preparation. Several schemes have been proposed for approximating...
Symul, Thomas, Alton, Daniel J., Assad, Syed M., Lance, Andrew M., Weedbrook, Christian, Ralph, Timothy C., ...
In realistic continuous variable quantum key distribution protocols, an eavesdropper may exploit the additional Gaussian noise generated during transmission to mask her presence. We present a...
Optical Zeno Gate: Bounds for Fault Tolerant Operation (2007)
Leung, Patrick M., Ralph, Timothy C.
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...
Jeong, Hyunseok, Ralph, Timothy C.
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...
Coherent State Distinguishability in Continuous Variable Quantum Cryptography (2007)
Weedbrook, Christian, Gu, Mile, Lance, Andrew M., Symul, Thomas, Lam, Ping Koy, Ralph, Timothy C.
We use the probability of error as a measure of distinguishability between two pure and two mixed symmetric coherent states in the context of continuous variable quantum cryptography. We show that...
Violation of Bell's inequality using classical measurements and non-linear local operations (2007)
Stobińska, Magdalena, Jeong, Hyunseok, Ralph, Timothy C.
We find that Bell's inequality can be significantly violated (up to Tsirelson's bound) with two-mode entangled coherent states using only homodyne measurements. This requires Kerr nonlinear...
Error propagation in loss- and failure-tolerant quantum computation schemes (2007)
Rohde, Peter P., Ralph, Timothy C., Munro, William J.
Qubit loss and gate failure are significant obstacles for the implementation of scalable quantum computation. Recently there have been several proposals for overcoming these problems, including...
Error tolerance and tradeoffs in loss- and failure-tolerant quantum computing schemes (2007)
Rohde, Peter P., Ralph, Timothy C., Munro, William J.
Qubit loss and gate failure are significant problems for the development of scalable quantum computing. Recently, various schemes have been proposed for tolerating qubit loss and gate failure. These...
Observation of a comb of optical squeezing over many gigahertz of bandwidth (2007)
Senior, R. J., Milford, G. N., Janousek, J., Dulop, A. E., Wagner, K., ...
We experimentally demonstrate the generation of optical squeezing at multiple longitudinal modes and transverse Hermite-Gauss modes of an optical parametric amplifier. We present measurements of...
Observation of a comb of optical squeezing over many gigahertz of bandwidth (2007)
Senior, R.J., Milford, G.N., Janousek, J., Dulop, A.E., Wagner, K., Bachor, H-A., ...
We experimentally demonstrate the generation of optical squeezing at multiple longitudinal modes and transverse Hermite-Gauss modes of an optical parametric amplifier. We present measurements of...
Error tolerance and tradeoffs in loss- and failure-tolerant quantum computing schemes (2007)
Rohde, Peter P., Ralph, Timothy C., Munro, William J.
Qubit loss and gate failure are significant problems for the development of scalable quantum computing. Recently, various schemes have been proposed for tolerating qubit loss and gate failure. These...
Observation of a comb of optical squeezing over many gigahertz of bandwidth (2007)
Senior, R. J., Milford, G. N., Janousek, J., Dulop, A. E., Wagner, K., ...
We experimentally demonstrate the generation of optical squeezing at multiple longitudinal modes and transverse Hermite-Gauss modes of an optical parametric amplifier. We present measurements of...
Measuring photon anti-bunching from continuous variable sideband squeezing (2006)
Grosse, Nicolai B., Symul, Thomas, Stobińska, Magdalena, Ralph, Timothy C., Lam, Ping Koy
We present a technique for measuring the second-order coherence function $g^{(2)}(\tau)$ of light using a Hanbury-Brown Twiss intensity interferometer modified for homodyne detection. The experiment...
Conditional quantum-state engineering using ancillary squeezed-vacuum states (2006)
Jeong, Hyunseok, Lance, Andrew M., Grosse, Nicolai B., Symul, Thomas, Lam, Ping Koy, Ralph, Timothy C.
We investigate an optical scheme to conditionally engineer quantum states using a beam splitter, homodyne detection and a squeezed vacuum as an ancillar state. This scheme is efficient in producing...
Universal Quantum Computation with Continuous-Variable Cluster States (2006)
Menicucci, Nicolas C., Van Loock, Peter, Gu, Mile, Weedbrook, Christian, Ralph, Timothy C., Nielsen, Michael A.
We describe a generalization of the cluster-state model of quantum computation to continuous-variable systems, along with a proposal for an optical implementation using squeezed-light sources, linear...
Error tolerance and tradeoffs in loss- and failure-tolerant quantum computing schemes (2006)
Rohde, Peter P., Ralph, Timothy C., Munro, William J.
Qubit loss and gate failure are significant problems for the development of scalable quantum computing. Recently various schemes have been proposed for tolerating qubit loss and gate failure. These...
Error models for mode-mismatch in linear optics quantum computing (2006)
Rohde, Peter P., Ralph, Timothy C.
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 State Engineering with Continuous-Variable Post-Selection (2005)
Lance, Andrew M., Jeong, Hyunseok, Grosse, Nicolai B., Symul, Thomas, Ralph, Timothy C., Lam, Ping Koy
We present a scheme to conditionally engineer an optical quantum system via continuous-variable measurements. This scheme yields high-fidelity squeezed single photon and superposition of coherent...
Practical limitations in optical entanglement purification (2005)
Rohde, Peter P., Ralph, Timothy C., Munro, William J.
Entanglement purification protocols play an important role in the distribution of entangled systems, which is necessary for various quantum information processing applications. We consider the...
Modeling photo-detectors in quantum optics (2005)
Rohde, Peter P., Ralph, Timothy C.
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...
Coherent State Quantum Key Distribution Without Random Basis Switching (2005)
Weedbrook, Christian, Lance, Andrew M., Bowen, Warwick P., Symul, Thomas, Ralph, Timothy C., Lam, Ping Koy
The random switching of measurement bases is commonly assumed to be a necessary step of quantum key distribution protocols. In this paper we show that switching is not required for coherent state...
Optimal photons for quantum information processing (2005)
Rohde, Peter P., Ralph, Timothy C., Nielsen, Michael A.
Photonic quantum information processing schemes, such as linear optics quantum computing, and other experiments relying on single-photon interference, inherently require complete photon...
No-Switching Quantum Key Distribution using Broadband Modulated Coherent Light (2005)
Lance, Andrew M., Symul, Thomas, Sharma, Vikram, Weedbrook, Christian, Ralph, Timothy C., Lam, Ping Koy
We realize an end-to-end no-switching quantum key distribution protocol using continuous-wave coherent light. We encode weak broadband Gaussian modulations onto the amplitude and phase quadratures of...
Quantum-gate characterization in an extended Hilbert space (2005)
Rohde, Peter P., Pryde, Geoff, O'Brien, J. L., Ralph, Timothy C.
We describe an approach for characterizing the process performed by a quantum gate using quantum process tomography, by first modeling the gate in an extended Hilbert space, which includes nonqubit...
Quantum-gate characterization in an extended Hilbert space (2005)
Rohde, Peter P., Pryde, Geoff, O'Brien, J. L., Ralph, Timothy C.
We describe an approach for characterizing the process performed by a quantum gate using quantum process tomography, by first modeling the gate in an extended Hilbert space, which includes nonqubit...
Quantum-gate characterization in an extended Hilbert space (2005)
Rohde, Peter P., Pryde, Geoff, O'Brien, J. L., Ralph, Timothy C.
We describe an approach for characterizing the process performed by a quantum gate using quantum process tomography, by first modeling the gate in an extended Hilbert space, which includes nonqubit...
Continuous Variable Quantum State Sharing via Quantum Disentanglement (2004)
Lance, Andrew M., Symul, Thomas, Bowen, Warwick P., Sanders, Barry C., Tyc, Tomas, Ralph, Timothy C., ...
Quantum state sharing is a protocol where perfect reconstruction of quantum states is achieved with incomplete or partial information in a multi-partite quantum networks. Quantum state sharing allows...
Quantum gate characterization in an extended Hilbert space (2004)
Rohde, Peter P., Pryde, G. J., O'Brien, J. L., Ralph, Timothy C.
We describe an approach for characterizing the process of quantum gates using quantum process tomography, by first modeling them in an extended Hilbert space, which includes non-qubit degrees of...
Jeong, Hyunseok, Ralph, Timothy C.
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...
Frequency and temporal effects in linear optical quantum computing (2004)
Rohde, Peter P., Ralph, Timothy C.
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...
Communicating continuous quantum variables between different Lorentz frames (2004)
Kok, Pieter, Ralph, Timothy C., Milburn, Gerard J.
We show how to communicate Heisenberg-limited continuous (quantum) variables between Alice and Bob in the case where they occupy two inertial reference frames that differ by an unknown Lorentz boost....
Quantum Cryptography without Switching (2004)
Weedbrook, Christian, Lance, Andrew M., Bowen, Warwick P., Symul, Thomas, Ralph, Timothy C., Lam, Ping Koy
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...
Experimental requirements for Grover's algorithm in optical quantum computation (2003)
Dodd, Jennifer L., Ralph, Timothy C., Milburn, G. J.
The field of linear optical quantum computation (LOQC) will soon need a repertoire of experimental milestones. We make progress in this direction by describing several experiments based on Grover's...
Experimental Requirements for Grover's Algorithm in Optical Quantum Computation (2003)
Dodd, Jennifer L., Ralph, Timothy C., Milburn, G. J.
The field of linear optical quantum computation (LOQC) will soon need a repertoire of experimental milestones. We make progress in this direction by describing several experiments based on Grover's...
Experimental Requirements for Grover's Algorithm in Optical Quantum Computation (2003)
Dodd, Jennifer L., Ralph, Timothy C., Milburn, G. J.
The field of linear optical quantum computation (LOQC) will soon need a repertoire of experimental milestones. We make progress in this direction by describing several experiments based on Grover's...
Continuous variable polarization entanglement, experiment and analysis (2003)
Bowen, Warwick P., Treps, Nicolas, Schnabel, Roman, Ralph, Timothy C., Lam, Ping Koy
We generate and characterise continuous variable polarization entanglement between two optical beams. We first produce quadrature entanglement, and by performing local operations we transform it into...
Stokes-operator-squeezed continuous-variable polarization states (2003)
Schnabel,Roman, Bowen,Warwick P., Treps,Nicolas, Ralph,Timothy C., Bachor,Hans-A., Lam,Ping Koy
We investigate nonclassical Stokes-operator variances in continuous-wave polarization-squeezed laser light generated from one and two optical parametric amplifiers. A general expression of how...
Optical experiments beyond the quantum limit: squeezing, entanglement and teleportation (2003)
Schnabel,Roman, Bowen,Warwick P., Treps,Nicolas, Ralph,Timothy C., Bachor,Hans-A., Lam,Ping Koy, ...
Stokes-operator-squeezed continuous-variable polarization states (2003)
Schnabel, Roman, Bowen, Warwick P., Treps, Nicolas, Ralph, Timothy C., Bachor, Hans-A., Lam, Ping Koy
We investigate nonclassical Stokes-operator variances in continuous-wave polarization-squeezed laser light generated from one and two optical parametric amplifiers. A general expression of how...
Optical experiments beyond the quantum limit: squeezing, entanglement and teleportation (2003)
Schnabel, Roman, Bowen, Warwick P., Treps, Nicolas, Ralph, Timothy C., Bachor, Hans-A., Lam, Ping Koy, ...
Experimental Requirements for Grover's Algorithm in Optical Quantum Computation (2003)
Dodd, Jennifer L., Ralph, Timothy C., Milburn, G. J.
The field of linear optical quantum computation (LOQC) will soon need a repertoire of experimental milestones. We make progress in this direction by describing several experiments based on Grover's...
Experimental Requirements for Grover's Algorithm in Optical Quantum Computation (2003)
Dodd, Jennifer L., Ralph, Timothy C., Milburn, G. J.
The field of linear optical quantum computation (LOQC) will soon need a repertoire of experimental milestones. We make progress in this direction by describing several experiments based on Grover's...
Stokes operator squeezed continuous variable polarization states (2002)
Schnabel, Roman, Bowen, Warwick P., Treps, Nicolas, Ralph, Timothy C., Bachor, Hans-A., Lam, Ping Koy
We investigate quantum correlations in continuous wave polarization squeezed laser light generated from one and two optical parametric amplifiers, respectively. A general expression of how Stokes...
Experimental investigation of continuous variable quantum teleportation (2002)
Bowen, Warwick P., Treps, Nicolas, Buchler, Ben C., Schnabel, Roman, Ralph, Timothy C., Bachor, Hans -A., ...
We report the experimental demonstration of quantum teleportation of the quadrature amplitudes of a light field. Our experiment was stably locked for long periods, and was analyzed in terms of...
Polarization squeezing and continuous-variable polarization entanglement (2001)
Korolkova, Natalia, Leuchs, Gerd, Loudon, Rodney, Ralph, Timothy C., Silberhorn, Christine
The Stokes-parameter operators and the associated Poincare sphere, which describe the quantum-optical polarization properties of light, are defined and their basic properties are reviewed. The...
Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback (1998)
Buchler, Ben C., Gray, Malcolm B., Shaddock, Daniel A., Ralph, Timothy C., McClelland, David E.
We present theoretical results that demonstrate a new technique to be used to improve the sensitivity of thermal noise measurements: intra-cavity intensity stabilisation. It is demonstrated that...
Noiseless phase quadrature amplification via electro-optic feed-forward (1998)
Buchler, Ben C., Huntington, Elanor H., Ralph, Timothy C.
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...