10,056 research outputs found
Disguising quantum channels by mixing and channel distance trade-off
We consider the reverse problem to the distinguishability of two quantum
channels, which we call the disguising problem. Given two quantum channels, the
goal here is to make the two channels identical by mixing with some other
channels with minimal mixing probabilities. This quantifies how much one
channel can disguise as the other. In addition, the possibility to trade off
between the two mixing probabilities allows one channel to be more preserved
(less mixed) at the expense of the other. We derive lower- and upper-bounds of
the trade-off curve and apply them to a few example channels. Optimal trade-off
is obtained in one example. We relate the disguising problem and the
distinguishability problem by showing the the former can lower and upper bound
the diamond norm. We also show that the disguising problem gives an upper bound
on the key generation rate in quantum cryptography.Comment: 27 pages, 8 figures. Added new results for using the disguising
problem to lower and upper bound the diamond norm and to upper bound the key
generation rate in quantum cryptograph
Time-Energy Costs of Quantum Measurements
Time and energy of quantum processes are a tradeoff against each other. We
propose to ascribe to any given quantum process a time-energy cost to quantify
how much computation it performs. Here, we analyze the time-energy costs for
general quantum measurements, along a similar line as our previous work for
quantum channels, and prove exact and lower bound formulae for the costs. We
use these formulae to evaluate the efficiencies of actual measurement
implementations. We find that one implementation for a Bell measurement is
optimal in time-energy. We also analyze the time-energy cost for unambiguous
state discrimination and find evidence that only a finite time-energy cost is
needed to distinguish any number of states.Comment: 10 pages, 6 figure
Time-Energy Measure for Quantum Processes
Quantum mechanics sets limits on how fast quantum processes can run given
some system energy through time-energy uncertainty relations, and they imply
that time and energy are tradeoff against each other. Thus, we propose to
measure the time-energy as a single unit for quantum channels. We consider a
time-energy measure for quantum channels and compute lower and upper bounds of
it using the channel Kraus operators. For a special class of channels (which
includes the depolarizing channel), we can obtain the exact value of the
time-energy measure. One consequence of our result is that erasing quantum
information requires times more time-energy resource than
erasing classical information, where is the system dimension.Comment: 13 pages, 2 figure
Entanglement transformation between sets of bipartite pure quantum states using local operations
Alice and Bob are given an unknown initial state chosen from a set of pure
quantum states. Their task is to transform the initial state to a corresponding
final pure state using local operations only. We prove necessary and sufficient
conditions on the existence of such a transformation. We also provide efficient
algorithms that can quickly rule out the possibility of transforming a set of
initial states to a set of final states.Comment: 19 pages, 1 figure, minor revision, to appear in J.Math.Phy
Supersymmetric Runge-Lenz-Pauli vector for Dirac vortex in topological insulators and graphene
The Dirac mass-vortex at the surface of a topological insulator or in
graphene is considered. Within the linear approximation for the vortex
amplitude's radial dependence, the spectrum is a series of degenerate bound
states, which can be classified by a set of accidental SU(2) and supersymmetry
generators (I. F. Herbut and C.-K. Lu, Phys. Rev. B 83 125412 (2011)). Here we
discuss further the properties and manifestations of the supersymmetry of the
vortex Hamiltonian, and point out some interesting analogies to the
Runge-Lenz-Pauli vector in the non-relativistic hydrogen atom. Symmetry
breaking effects due to a finite chemical potential, and the Zeeman field are
also analyzed. We find that a residual accidental degeneracy remains only in
the special case of equal magnitudes of both terms, whereas otherwise it
becomes removed entirely.Comment: revised version with added reference and a new paragraph on
interpretation of two-velocity Weyl fermions realized in 2D optical lattice;
to appear in J Phys
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Author name used in this publication: David Dagan FengAuthor name used in this publication: Zheru ChiRefereed conference paper2000-2001 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Large Universality of The Baryon Isgur--Wise Form Factor: The Group Theoretical Approach
In a previous article, it has been proved under the framework of chiral
soliton model that the same Isgur--Wise form factor describes the semileptonic
and decays in the
large limit. It is shown here that this result is in fact independent of
the chiral soliton model and is solely the consequence of the spin-flavor SU(4)
symmetry which arises in the baryon sector in the large limit.Comment: 10 pages in REVTeX, no figure
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