179 research outputs found
Accelerated Detectors and Temperature in (Anti) de Sitter Spaces
We show, in complete accord with the usual Rindler picture, that detectors
with constant acceleration in de Sitter (dS) and Anti de Sitter (AdS)
spaces with cosmological constants measure temperatures , the detector "5-acceleration" in the
embedding flat 5-space. For dS, this recovers a known result; in AdS, where
is negative, the temperature is well defined down to the critical
value , again in accord with the underlying kinematics. The existence
of a thermal spectrum is also demonstrated for a variety of candidate wave
functions in AdS backgrounds.Comment: Latex +2 Fi
The state space for two qutrits has a phase space structure in its core
We investigate the state space of bipartite qutrits. For states which are
locally maximally mixed we obtain an analog of the ``magic'' tetrahedron for
bipartite qubits--a magic simplex W. This is obtained via the Weyl group which
is a kind of ``quantization'' of classical phase space. We analyze how this
simplex W is embedded in the whole state space of two qutrits and discuss
symmetries and equivalences inside the simplex W. Because we are explicitly
able to construct optimal entanglement witnesses we obtain the border between
separable and entangled states. With our method we find also the total area of
bound entangled states of the parameter subspace under intervestigation. Our
considerations can also be applied to higher dimensions.Comment: 3 figure
The unmasking of thermal Goldstone bosons
The problem of extracting the modes of Goldstone bosons from a thermal
background is reconsidered in the framework of relativistic quantum field
theory. It is shown that in the case of spontaneous breakdown of an internal
bosonic symmetry a recently established decomposition of thermal correlation
functions contains certain specific contributions which can be attributed to a
particle of zero mass.Comment: 7 pages, LaTeX; new and considerably strengthened results after Eq.
(14); to appear in Phys. Rev.
The Reeh-Schlieder property for thermal field theories
We show that the Reeh-Schlieder property w.r.t. the KMS-vector is a direct
consequence of locality, additivity and the relativistic KMS-condition. The
latter characterises the thermal equilibrium states of a relativistic quantum
field theory. The statement remains vaild even if the given equilibrium state
breaks spatial translation invariance.Comment: plain tex, 10 page
A special simplex in the state space for entangled qudits
Focus is on two parties with Hilbert spaces of dimension d, i.e. "qudits". In
the state space of these two possibly entangled qudits an analogue to the well
known tetrahedron with the four qubit Bell states at the vertices is presented.
The simplex analogue to this magic tetrahedron includes mixed states. Each of
these states appears to each of the two parties as the maximally mixed state.
Some studies on these states are performed, and special elements of this set
are identified. A large number of them is included in the chosen simplex which
fits exactly into conditions needed for teleportation and other applications.
Its rich symmetry - related to that of a classical phase space - helps to study
entanglement, to construct witnesses and perform partial transpositions. This
simplex has been explored in details for d=3. In this paper the mathematical
background and extensions to arbitrary dimensions are analysed.Comment: 24 pages, in connection with the Workshop 'Theory and Technology in
Quantum Information, Communication, Computation and Cryptography' June 2006,
Trieste; summary and outlook added, minor changes in notatio
A quantum fluctuation description of charge qubits
We consider a specific instance of a superconducting circuit, the so-called
charge-qubit, consisting of a capacitor and a Josephson junction. Starting from
the microscopic description of the latter in terms of two tunneling BCS models
in the strong-coupling quasi-spin formulation, we derive the Hamiltonian
governing the quantum behavior of the circuit in the limit of a large number
of quasi-spins. Our approach relies on the identification of suitable
quantum fluctuations, i.e. of collective quasi-spin operators, which account
for the presence of fluctuation operators in the superconducting phase that
retain a quantum character in spite of the large- limit. We show indeed that
these collective quantum fluctuations generate the Heisenberg algebra on the
circle and that their dynamics reproduces the one of the quantized
charge-qubit, without the need of a phenomenological ``third quantization'' of
a semiclassically inspired model. As a byproduct of our derivation, we
explicitly obtain the temperature dependence of the junction critical Josephson
current in the strong coupling regime, a result which is not directly
accessible using standard approximation techniques.Comment: 34 page
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