



01338nas a2200157   4500008004100000245004300041210004200084260001500126300001200141490000700153520091300160100002301073700002201096700001801118856004401136       2006                        eng d00aTwo-way quantum communication channels0 aTwoway quantum communication channels  c2006/02/01  a63 - 830 v043 a  We consider communication between two parties using a bipartite quantum
operation, which constitutes the most general quantum mechanical model of
two-party communication. We primarily focus on the simultaneous forward and
backward communication of classical messages. For the case in which the two
parties share unlimited prior entanglement, we give inner and outer bounds on
the achievable rate region that generalize classical results due to Shannon. In
particular, using a protocol of Bennett, Harrow, Leung, and Smolin, we give a
one-shot expression in terms of the Holevo information for the
entanglement-assisted one-way capacity of a two-way quantum channel. As
applications, we rederive two known additivity results for one-way channel
capacities: the entanglement-assisted capacity of a general one-way channel,
and the unassisted capacity of an entanglement-breaking one-way channel.
1 aChilds, Andrew, M.1 aLeung, Debbie, W.1 aLo, Hoi-Kwong  uhttp://arxiv.org/abs/quant-ph/0506039v101341nas a2200145   4500008004100000245007700041210006900118260001400187490000700201520087300208100002301081700002201104700002501126856004401151       2005                        eng d00aUnified derivations of measurement-based schemes for quantum computation0 aUnified derivations of measurementbased schemes for quantum comp  c2005/3/170 v713 a  We present unified, systematic derivations of schemes in the two known
measurement-based models of quantum computation. The first model (introduced by
Raussendorf and Briegel [Phys. Rev. Lett., 86, 5188 (2001)]) uses a fixed
entangled state, adaptive measurements on single qubits, and feedforward of the
measurement results. The second model (proposed by Nielsen [Phys. Lett. A, 308,
96 (2003)] and further simplified by Leung [Int. J. Quant. Inf., 2, 33 (2004)])
uses adaptive two-qubit measurements that can be applied to arbitrary pairs of
qubits, and feedforward of the measurement results. The underlying principle of
our derivations is a variant of teleportation introduced by Zhou, Leung, and
Chuang [Phys. Rev. A, 62, 052316 (2000)]. Our derivations unify these two
measurement-based models of quantum computation and provide significantly
simpler schemes.
1 aChilds, Andrew, M.1 aLeung, Debbie, W.1 aNielsen, Michael, A.  uhttp://arxiv.org/abs/quant-ph/0404132v201270nas a2200157   4500008004100000245006000041210006000101260001500161300001600176490000700192520080600199100002301005700002201028700001801050856004401068       2004                        eng d00aReversible simulation of bipartite product Hamiltonians0 aReversible simulation of bipartite product Hamiltonians  c2004/06/01  a1189 - 11970 v503 a  Consider two quantum systems A and B interacting according to a product
Hamiltonian H = H_A x H_B. We show that any two such Hamiltonians can be used
to simulate each other reversibly (i.e., without efficiency losses) with the
help of local unitary operations and local ancillas. Accordingly, all non-local
features of a product Hamiltonian -- including the rate at which it can be used
to produce entanglement, transmit classical or quantum information, or simulate
other Hamiltonians -- depend only upon a single parameter. We identify this
parameter and use it to obtain an explicit expression for the entanglement
capacity of all product Hamiltonians. Finally, we show how the notion of
simulation leads to a natural formulation of measures of the strength of a
nonlocal Hamiltonian.
1 aChilds, Andrew, M.1 aLeung, Debbie, W.1 aVidal, Guifre  uhttp://arxiv.org/abs/quant-ph/0303097v101006nas a2200145   4500008004100000245005300041210005300094260001400147490000700161520058100168100002300749700002200772700002200794856004400816       2001                        eng d00aRealization of quantum process tomography in NMR0 aRealization of quantum process tomography in NMR  c2001/6/130 v643 a  Quantum process tomography is a procedure by which the unknown dynamical
evolution of an open quantum system can be fully experimentally characterized.
We demonstrate explicitly how this procedure can be implemented with a nuclear
magnetic resonance quantum computer. This allows us to measure the fidelity of
a controlled-not logic gate and to experimentally investigate the error model
for our computer. Based on the latter analysis, we test an important assumption
underlying nearly all models of quantum error correction, the independence of
errors on different qubits.
1 aChilds, Andrew, M.1 aChuang, Isaac, L.1 aLeung, Debbie, W.  uhttp://arxiv.org/abs/quant-ph/0012032v101258nas a2200181   4500008004100000245005500041210005500096260001400151490000700165520074300172100001600915700002300931700002200954700001700976700002200993700001701015856004401032       2001                        eng d00aUniversal simulation of Markovian quantum dynamics0 aUniversal simulation of Markovian quantum dynamics  c2001/11/90 v643 a  Although the conditions for performing arbitrary unitary operations to
simulate the dynamics of a closed quantum system are well understood, the same
is not true of the more general class of quantum operations (also known as
superoperators) corresponding to the dynamics of open quantum systems. We
propose a framework for the generation of Markovian quantum dynamics and study
the resources needed for universality. For the case of a single qubit, we show
that a single nonunitary process is necessary and sufficient to generate all
unital Markovian quantum dynamics, whereas a set of processes parametrized by
one continuous parameter is needed in general. We also obtain preliminary
results for the unital case in higher dimensions.
1 aBacon, Dave1 aChilds, Andrew, M.1 aChuang, Isaac, L.1 aKempe, Julia1 aLeung, Debbie, W.1 aZhou, Xinlan  uhttp://arxiv.org/abs/quant-ph/0008070v2