Conference

Displaying 4513 - 4524 of 4905

Toward a quantum Fourier transform on SU(2).

Richard Low Apple Inc.
June 04, 2007

PIRSA:07060023
Quantum Physics
Categorizing nonclassical phenomena: the explanatory power of epistemic restrictions and contextuality

Robert Spekkens Perimeter Institute for Theoretical Physics
June 04, 2007

PIRSA:07060037
Quantum Physics

Quantum Physics
Approximate quantum encryption and entropic security

Frédéric Dupuis McGill University
June 04, 2007

PIRSA:07060022
Quantum Physics
Practical quantum-key-distribution systems with detector efficiency mismatch: attacks and secret key rates
June 04, 2007

PIRSA:07060021
Quantum Physics
Learning about topological quantum memory

Lucy Liuxuan Zhang University of Maryland, College Park
June 04, 2007

PIRSA:07060020
Quantum Physics
Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source

Christopher Erven Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060050
Quantum Physics
Symmetric extendibility of quantum states

Geir Myhr Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060019
Quantum Physics
Classical Post-processing for Low-Depth Phase Estimation Circuits

Donny Cheung Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060018
Quantum Physics
Coherent Control with Time-Energy entangled photons

Yaron Bromberg Weizmann Institute of Science
June 03, 2007

PIRSA:07060017
Quantum Physics
Quantum Cellular Automata Applications

Carlos Perez Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060049
Quantum Physics
Multiplicativity and Strong Multiplicativity of Norms on Transformations

Bill Rosgen Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060016
Quantum Physics
Purifying qubits in NMR quantum information processing

Colm Ryan Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060015
Quantum Physics

Toward a quantum Fourier transform on SU(2).

Richard Low Apple Inc.
June 04, 2007

PIRSA:07060023
Quantum Physics
Almost all known superpolynomial quantum speedups over classical algorithms have used the quantum Fourier transform (QFT). Most known applications of the QFT make use of the QFT over abelian groups, including Shor’s well known factoring algorithm [1]. However, the QFT can be generalised to act on non-abelian groups allowing different applications. For example, Kuperberg solves the dihedral hidden subgroup problem in subexponential time using the QFT on the dihedral group. The aim of this research is to construct an efficient QFT on SU(2). Most of the progress in constructing QFTs has come from applying ideas from classical algorithms such as subgroup adapted bases. For example, Moore et al. have applied classical ideas from e.g. to build non-abelian QFTs. Applying these ideas to infinite groups such as SU(2) requires new tools. The function must be sampled or discretised in a way so as to minimise the error. I will present some ideas based on classical algorithms which may lead to a QFT over the group SU(2) for band limited functions. There are problems with making these algorithms unitary that must be addressed and efficient methods for calculating coefficients (cf. the controlled phase gates in the abelian case) must be found.
Categorizing nonclassical phenomena: the explanatory power of epistemic restrictions and contextuality

Robert Spekkens Perimeter Institute for Theoretical Physics
June 04, 2007

PIRSA:07060037
Quantum Physics

Quantum Physics
Approximate quantum encryption and entropic security

Frédéric Dupuis McGill University
June 04, 2007

PIRSA:07060022
Quantum Physics
An approximate quantum encryption scheme uses a private key to encrypt a quantum state while leaking only a very small (though non-zero) amount of information to the adversary. Previous work has shown that while we need 2n bits of key to encrypt n qubits exactly, we can get away with only n bits in the approximate case, provided that we know that the state to be encrypted is not entangled with something that the adversary already has in his possession. In this talk I will show a generalization of this result: approximate quantum encryption requires roughly n-t bits of key, where t is a lower bound on the conditional min-entropy of the state to be encrypted given the adversary's prior knowledge. Along the way, I will introduce a quantum version of entropic security and show how the approximate quantum encryption scheme fits within this framework. This is joint work with Simon-Pierre Desrosiers.
Practical quantum-key-distribution systems with detector efficiency mismatch: attacks and secret key rates
June 04, 2007

PIRSA:07060021
Quantum Physics
Imperfections in devices are inevitable in practice. In this talk, we focus on the imperfection of QKD systems in the detectors, namely that the efficiencies of the detectors are not completely identical. We show some practical attacks that specifically exploit this efficiency mismatch and demonstrate how Eve may obtain some information on the final key if Alice and Bob are unaware of the attack. Also, we discuss the upper and lower bounds on the secret key rates both with and without the assumption of the efficiency mismatch
Learning about topological quantum memory

Lucy Liuxuan Zhang University of Maryland, College Park
June 04, 2007

PIRSA:07060020
Quantum Physics
I will introduce Kitaev's suface codes as a block quantum error-correcting code. Recovery procedures will be described in the case of imperfect syndrome measurements. More might be covered if time permits.
Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source

Christopher Erven Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060050
Quantum Physics
Symmetric extendibility of quantum states

Geir Myhr Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060019
Quantum Physics
Imagine that Alice and Bob share a quantum state, from which they want to distill something useful like entanglement or secret key. For this they need to communicate classically and they want to do this by one way communication from Alice to Bob. For some states, it might happen that the state is a part of a tripartite state shared with Charlie, which is invariant if Bob's and Charlie's systems are switched. Such a state is called a symmetric extension, and if it exists Alice and Bob have no chance of distilling key or entanglement by one way communication. I will present some results characterizing which quantum states have symmetric extension.
Classical Post-processing for Low-Depth Phase Estimation Circuits

Donny Cheung Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060018
Quantum Physics
Traditionally, we use the quantum Fourier transform circuit (QFT) in order to perform quantum phase estimation, which has a number of useful applications. The QFT circuit for a binary field generally consists controlled-rotation gates which, when removed, yields the lower-depth approximate QFT circuit. It is known that a logarithmic-depth approximate QFT circuit is sufficient to perform phase estimation with a degree of accuracy negligibly lower than that of the full QFT. However, when the depth of the AQFT circuit becomes even lower, the phase estimation procedure no longer produces results that are immediately correlated to the desired phase. In this talk, I will explore the possibility of retrieving this information with classical analysis and with computer post-processing of the measured results of a low-depth AQFT circuit in a phase estimation algorithm.
Coherent Control with Time-Energy entangled photons

Yaron Bromberg Weizmann Institute of Science
June 03, 2007

PIRSA:07060017
Quantum Physics
"Most of the experimental advances in coherent quantum control in recent years have involved ultrashort pulses and pulse shaping techniques. These pulses have been an excellent source of coherent light with precise phase relationship between the various frequency components. In several recent works we have investigated the possibility of using broadband nonclassical light, generated by down-conversion of narrow-band lasers, for coherent control.We demonstrated that pulse shaping techniques can be used in the single-photon limit, when the light is composed of individual time-energy entangled photons. We could shape the two-photon correlation function, which is as close as one can get to ‘shaping of individual photons’. Using polarization pulse-shaping techniques we also controlled the quantum interference of polarization entangled photons. By controlling both phase and polarization of the photon-pairs, we were able to tailor the Hong-Ou-Mandel interference pattern, and generate all four polarization Bell-states.We believe that the combination of quantum control techniques with quantum optics could add an important ingredient to the toolbox of quantum information and computing."
Quantum Cellular Automata Applications

Carlos Perez Institute for Quantum Computing (IQC)
June 03, 2007

PIRSA:07060049
Quantum Physics
Multiplicativity and Strong Multiplicativity of Norms on Transformations

Bill Rosgen Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060016
Quantum Physics
Proving the additivity of the classical capacity of quantum channels is a major open problem in quantum information. This problem is related to the multiplicativity of certain norms with respect to the tensor product. These problems are introduced and some approached to resolving them are discussed. Several special cases that have been solved are also mentioned.
Purifying qubits in NMR quantum information processing

Colm Ryan Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060015
Quantum Physics
Any implementation of a quantum computer will require the ability to reset qubits to a pure input state, both to start the computation and more importantly to implement fault-tolerant operations. Even if we cannot reset to a perfectly pure state, heat-bath algorithmic cooling provides a method of purifying mixed states. By combining the ability to pump entropy out of the system through a controllable interaction with a heat bath and coherent control of the qubits, we are able to cool a subset of the qubits far below the heat bath temperature. Here we show an implementation of this cooling in a solid state NMR quantum information processor which offers high fidelity control of the qubit system and controllable access to a heat bath. We demonstrate an implementation of multiple rounds of heat-bath algorithmic cooling on three qubits and discuss the improvements in control techniques which have allowed us to show the purification of a single qubit to one and a half times the heat bath polarization.

Title	Speaker(s)	Date	Talk Type	Info link
Toward a quantum Fourier transform on SU(2).	Richard Low	2007-06-04	Conference	View details
Categorizing nonclassical phenomena: the explanatory power of epistemic restrictions and contextuality	Robert Spekkens	2007-06-04	Conference	View details
Approximate quantum encryption and entropic security	Frédéric Dupuis	2007-06-04	Conference	View details
Practical quantum-key-distribution systems with detector efficiency mismatch: attacks and secret key rates		2007-06-04	Conference	View details
Learning about topological quantum memory	Lucy Liuxuan Zhang	2007-06-04	Conference	View details
Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source	Christopher Erven	2007-06-03	Conference	View details
Symmetric extendibility of quantum states	Geir Myhr	2007-06-03	Conference	View details
Classical Post-processing for Low-Depth Phase Estimation Circuits	Donny Cheung	2007-06-03	Conference	View details
Coherent Control with Time-Energy entangled photons	Yaron Bromberg	2007-06-03	Conference	View details
Quantum Cellular Automata Applications	Carlos Perez	2007-06-03	Conference	View details
Multiplicativity and Strong Multiplicativity of Norms on Transformations	Bill Rosgen	2007-06-02	Conference	View details
Purifying qubits in NMR quantum information processing	Colm Ryan	2007-06-02	Conference	View details

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Format results

Toward a quantum Fourier transform on SU(2).

Categorizing nonclassical phenomena: the explanatory power of epistemic restrictions and contextuality

Approximate quantum encryption and entropic security

Practical quantum-key-distribution systems with detector efficiency mismatch: attacks and secret key rates

Learning about topological quantum memory

Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source

Symmetric extendibility of quantum states

Classical Post-processing for Low-Depth Phase Estimation Circuits

Coherent Control with Time-Energy entangled photons

Quantum Cellular Automata Applications

Multiplicativity and Strong Multiplicativity of Norms on Transformations

Purifying qubits in NMR quantum information processing

Toward a quantum Fourier transform on SU(2).

Categorizing nonclassical phenomena: the explanatory power of epistemic restrictions and contextuality

Approximate quantum encryption and entropic security

Practical quantum-key-distribution systems with detector efficiency mismatch: attacks and secret key rates

Learning about topological quantum memory

Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source

Symmetric extendibility of quantum states

Classical Post-processing for Low-Depth Phase Estimation Circuits

Coherent Control with Time-Energy entangled photons

Quantum Cellular Automata Applications

Multiplicativity and Strong Multiplicativity of Norms on Transformations

Purifying qubits in NMR quantum information processing