122 research outputs found
Optimum unambiguous identification of d unknown pure qudit states
We address the problem of unambiguously identifying the state of a probe
qudit with the state of one of d reference qudits. The reference states are
assumed pure and linearly independent but we have no knowledge of them. The
state of the probe qudit is assumed to coincide equally likely with either one
of the d unknown reference states. We derive the optimum measurement strategy
that maximizes the success probability of unambiguous identification and find
that the optimum strategy is a generalized measurement. We give both the
measurement operators and the optimum success probability explicitly.
Technically, the problem we solve amounts to the optimum unambiguous
discrimination of d known mixed quantum states.Comment: A reference has been included and a sign error has been corrected
that propagated and affected the final result and is unfortunately also
present in the printed journal versio
Optimized maximum-confidence discrimination of N mixed quantum states and application to symmetric states
We study an optimized measurement which discriminates N mixed quantum states
occurring with given prior robabilities. The measurement yields the maximum
achievable confidence for each of the N conclusive outcomes, thereby keeping
the overall probability of inconclusive outcomes as small as possible. It
corresponds to optimum unambiguous discrimination when for each outcome the
confidence is equal to unity. Necessary and sufficient optimality conditions
are derived and general properties of the optimum measurement are obtained. The
results are applied to the optimized maximum-confidence discrimination of N
equiprobable symmetric mixed states. Analytical solutions are presented for a
number of examples, including the discrimination of N symmetric pure states
spanning a d-dimensional Hilbert space (d \leq N) and the discrimination of N
symmetric mixed qubit states.Comment: minor corrections, final versio
Single-photon generation and simultaneous observation of wave and particle properties
We describe an experiment that generates single photons on demand and
measures properties accounted to both particle- and wave-like features of
light. The measurement is performed by exploiting data that are sampled
simultaneously in a single experimental run.Comment: The following article has been submitted to Proceedings of
"Foundations of probability and physics-3", Vaxjo, Sweden 2004. After it is
published, it will be found at http://proceedings.aip.org/ . 1 Reference was
added in version
Discrimination of two mixed quantum states with maximum confidence and minimum probability of inconclusive results
We study an optimized measurement that discriminates two mixed quantum states
with maximum confidence for each conclusive result, thereby keeping the overall
probability of inconclusive results as small as possible. When the rank of the
detection operators associated with the two different conclusive outcomes does
not exceed unity we obtain a general solution. As an application, we consider
the discrimination of two mixed qubit states. Moreover, for the case of
higher-rank detection operators we give a solution for particular states. The
relation of the optimized measurement to other discrimination schemes is also
discussed.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.
Distinguishing mixed quantum states: Minimum-error discrimination versus optimum unambiguous discrimination
We consider two different optimized measurement strategies for the
discrimination of nonorthogonal quantum states. The first is conclusive
discrimination with a minimum probability of inferring an erroneous result, and
the second is unambiguous, i. e. error-free, discrimination with a minimum
probability of getting an inconclusive outcome, where the measurement fails to
give a definite answer. For distinguishing between two mixed quantum states, we
investigate the relation between the minimum error probability achievable in
conclusive discrimination, and the minimum failure probability that can be
reached in unambiguous discrimination of the same two states. The latter turns
out to be at least twice as large as the former for any two given states. As an
example, we treat the case that the state of the quantum system is known to be,
with arbitrary prior probability, either a given pure state, or a uniform
statistical mixture of any number of mutually orthogonal states. For this case
we derive an analytical result for the minimum probability of error and perform
a quantitative comparison to the minimum failure probability.Comment: Replaced by final version, accepted for publication in Phys. Rev. A.
Revtex4, 6 pages, 3 figure
Optimum unambiguous discrimination of two mixed states and application to a class of similar states
We study the measurement for the unambiguous discrimination of two mixed
quantum states that are described by density operators and of
rank d, the supports of which jointly span a 2d-dimensional Hilbert space.
Based on two conditions for the optimum measurement operators, and on a
canonical representation for the density operators of the states, two equations
are derived that allow the explicit construction of the optimum measurement,
provided that the expression for the fidelity of the states has a specific
simple form. For this case the problem is mathematically equivalent to
distinguishing pairs of pure states, even when the density operators are not
diagonal in the canonical representation. The equations are applied to the
optimum unambiguous discrimination of two mixed states that are similar states,
given by , and that belong to the class where the
unitary operator U can be decomposed into multiple rotations in the d mutually
orthogonal two-dimensional subspaces determined by the canonical
representation.Comment: 8 pages, changes in title and presentatio
A folded-sandwich polarization-entangled two-color photon pair source with large tuning capability for applications in hybrid quantum architectures
We demonstrate a two-color entangled pho ton pair source which can be adapted
easily to a wide range of wavelengths combinations. A Fresnel rhomb as a
geometrical quarter-wave plate and a versatile combination of compensation
crystals are key components of the source. Entanglement of two photons at the
Cs D1 line (894.3 nm) and at the telecom O-band (1313.1 nm) with a fidelity of
is demonstrated and improvements of the setup are
discussed
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