12,917 research outputs found
One-shot rates for entanglement manipulation under non-entangling maps
We obtain expressions for the optimal rates of one- shot entanglement
manipulation under operations which generate a negligible amount of
entanglement. As the optimal rates for entanglement distillation and dilution
in this paradigm, we obtain the max- and min-relative entropies of
entanglement, the two logarithmic robustnesses of entanglement, and smoothed
versions thereof. This gives a new operational meaning to these entanglement
measures. Moreover, by considering the limit of many identical copies of the
shared entangled state, we partially recover the recently found reversibility
of entanglement manipu- lation under the class of operations which
asymptotically do not generate entanglement.Comment: 7 pages; no figure
Designing protein β-sheet surfaces by Z-score optimization
Studies of lattice models of proteins have suggested that the appropriate energy expression for protein design may include nonthermodynamic terms to accommodate negative design concerns. One method, developed in lattice model studies, maximizes a quantity known as the "Z-score," which compares the lowest energy sequence whose ground state structure is the target structure to an ensemble of random sequences. Here we show that, in certain circumstances, the technique can be applied to real proteins. The resulting energy expression is used to design the β-sheet surfaces of two real proteins. We find experimentally that the designed proteins are stable and well folded, and in one case is even more thermostable than the wild type
Orthogonal measurements are {\it almost} sufficient for quantum discord of two qubits
The common use in literature of orthogonal measurements in obtaining quantum
discord for two-qubit states is discussed and compared with more general
measurements. We prove the optimality of orthogonal measurements for rank 2
states. While for rank 3 and 4 mixed states they are not optimal, we present
strong numerical evidence showing that they give the correct quantum discord up
to minimal corrections. Based on the connection, through purification with an
ancilla, between discord and entanglement of formation (EoF), we give a tight
upper bound for the EoF of a mixed state of rank 2, given by an
optimal decomposition of 2 elements. We also provide an alternative way to
compute the quantum discord for two qubits based on the Bloch vectors of the
state.Comment: EPL 96, 40005 (2011
A smooth entropy approach to quantum hypothesis testing and the classical capacity of quantum channels
We use the smooth entropy approach to treat the problems of binary quantum
hypothesis testing and the transmission of classical information through a
quantum channel. We provide lower and upper bounds on the optimal type II error
of quantum hypothesis testing in terms of the smooth max-relative entropy of
the two states representing the two hypotheses. Using then a relative entropy
version of the Quantum Asymptotic Equipartition Property (QAEP), we can recover
the strong converse rate of the i.i.d. hypothesis testing problem in the
asymptotics. On the other hand, combining Stein's lemma with our bounds, we
obtain a stronger (\ep-independent) version of the relative entropy-QAEP.
Similarly, we provide bounds on the one-shot \ep-error classical capacity of
a quantum channel in terms of a smooth max-relative entropy variant of its
Holevo capacity. Using these bounds and the \ep-independent version of the
relative entropy-QAEP, we can recover both the Holevo-Schumacher-Westmoreland
theorem about the optimal direct rate of a memoryless quantum channel with
product state encoding, as well as its strong converse counterpart.Comment: v4: Title changed, improved bounds, both direct and strong converse
rates are covered, a new Discussion section added. 20 page
M-atom conductance oscillations of a metallic quantum wire
The electron transport through a monoatomic metallic wire connected to leads
is investigated using the tight-binding Hamiltonian and Green's function
technique. Analytical formulas for the transmittance are derived and M-atom
oscillations of the conductance versus the length of the wire are found. Maxima
of the transmittance function versus the energy, for the wire consisted of N
atoms, determine the (N+1) period of the conductance. The periods of
conductance oscillations are discussed and the local and average quantum wire
charges are presented. The average charge of the wire is linked with the period
of the conductance oscillations and it tends to the constant value as the
length of the wire increases. For M-atom periodicity there are possible (M-1)
average occupations of the wire states.Comment: 8 pages, 5 figures. J.Phys.: Condens. matter (2005) accepte
Phonon runaway in nanotube quantum dots
We explore electronic transport in a nanotube quantum dot strongly coupled
with vibrations and weakly with leads and the thermal environment. We show that
the recent observation of anomalous conductance signatures in single-walled
carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms
of current driven `hot phonons' that are strongly correlated with electrons.
Using rate equations in the many-body configuration space for the joint
electron-phonon distribution, we argue that the variations are indicative of
strong electron-phonon coupling requiring an analysis beyond the traditional
uncorrelated phonon-assisted transport (Tien-Gordon) approach.Comment: 8 pages, 6 figure
Partitioning technique for a discrete quantum system
We develop the partitioning technique for quantum discrete systems. The graph
consists of several subgraphs: a central graph and several branch graphs, with
each branch graph being rooted by an individual node on the central one. We
show that the effective Hamiltonian on the central graph can be constructed by
adding additional potentials on the branch-root nodes, which generates the same
result as does the the original Hamiltonian on the entire graph. Exactly
solvable models are presented to demonstrate the main points of this paper.Comment: 7 pages, 2 figure
Mesoscopic Resistance Fluctuations in Cobalt Nanoparticles
We present measurements of mesoscopic resistance fluctuations in cobalt
nanoparticles and study how the fluctuations with bias voltage, bias
fingerprints, respond to magnetization reversal processes. Bias fingerprints
rearrange when domains are nucleated or annihilated. The domain-wall causes an
electron wavefunction phase-shift of . The phase-shift is not
caused by the Aharonov-Bohm effect; we explain how it arises from the
mistracking effect, where electron spins lag in orientation with respect to the
moments inside the domain-wall. Dephasing time in Co at is short,
, which we attribute to the strong magnetocrystalline
anisotropy.Comment: 5 pages 3 figs colou
Effect of dephasing on the current statistics of mesoscopic devices
We investigate the effects of dephasing on the current statistics of
mesoscopic conductors with a recently developed statistical model, focusing in
particular on mesoscopic cavities and Aharonov-Bohm rings. For such devices, we
analyze the influence of an arbitrary degree of decoherence on the cumulants of
the current. We recover known results for the limiting cases of fully coherent
and totally incoherent transport and are able to obtain detailed information on
the intermediate regime of partial coherence for a varying number of open
channels. We show that dephasing affects the average current, shot noise, and
higher order cumulants in a quantitatively and qualitatively similar way, and
that consequently shot noise or higher order cumulants of the current do not
provide information on decoherence additional or complementary to what can be
already obtained from the average current.Comment: 4 pages, 4 figure
A 233 km Tunnel for Lepton and Hadron Colliders
A decade ago, a cost analysis was conducted to bore a 233 km circumference
Very Large Hadron Collider (VLHC) tunnel passing through Fermilab. Here we
outline implementations of , , and collider
rings in this tunnel using recent technological innovations. The 240 and 500
GeV colliders employ Crab Waist Crossings, ultra low emittance damped
bunches, short vertical IP focal lengths, superconducting RF, and low
coercivity, grain oriented silicon steel/concrete dipoles. Some details are
also provided for a high luminosity 240 GeV collider and 1.75 TeV
muon accelerator in a Fermilab site filler tunnel. The 40 TeV
collider uses the high intensity Fermilab source, exploits high cross
sections for production of high mass states, and uses 2 Tesla ultra
low carbon steel/YBCO superconducting magnets run with liquid neon. The 35 TeV
muon ring ramps the 2 Tesla superconducting magnets at 9 Hz every 0.4 seconds,
uses 250 GV of superconducting RF to accelerate muons from 1.75 to 17.5 TeV in
63 orbits with 71% survival, and mitigates neutrino radiation with phase
shifting, roller coaster motion in a FODO lattice.Comment: LaTex, 6 pages, 1 figure, Advanced Accelerator Concepts Workshop,
Austin, TX, 10-15 June 201
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