493 research outputs found
K+(K0)- Condensation in Highly Dense Matter with the Relativistic Mean-Field Theory
Properties of dense hadronic matter including strange particles are studied
within the relativistic mean-field theory (RMFT). The possibility of kaon
condensation is reexamined, and a simple condition is found for the parameters
included in RMFT.Comment: 12pages, Latex is used, 3 Postscript figures are available by request
from [email protected]
Topologically protected measurement-based quantum computation on the thermal state of a nearest-neighbor two-body Hamiltonian with spin-3/2 particles
Recently, Li {\it et al.} [Phys. Rev. Lett. {\bf 107}, 060501 (2011)] have
demonstrated that topologically protected measurement-based quantum computation
can be implemented on the thermal state of a nearest-neighbor two-body
Hamiltonian with spin-2 and spin-3/2 particles provided that the temperature is
smaller than a critical value, namely, threshold temperature. Here we show that
the thermal state of a nearest-neighbor two-body Hamiltonian, which consists of
only spin-3/2 particles, allows us to perform topologically protected
measurement-based quantum computation. The threshold temperature is calculated
and turns out to be comparable to that with the spin-2 and spin-3/2 system.
Furthermore, we generally show that a cluster state of high connectivity can be
efficiently generated from the thermal state of the spin-3/2 system without
severe thermal noise accumulation.Comment: 5 pages, 2 figures; v2 published versio
Blind quantum computation protocol in which Alice only makes measurements
Blind quantum computation is a new secure quantum computing protocol which
enables Alice who does not have sufficient quantum technology to delegate her
quantum computation to Bob who has a fully-fledged quantum computer in such a
way that Bob cannot learn anything about Alice's input, output, and algorithm.
In previous protocols, Alice needs to have a device which generates quantum
states, such as single-photon states. Here we propose another type of blind
computing protocol where Alice does only measurements, such as the polarization
measurements with a threshold detector. In several experimental setups, such as
optical systems, the measurement of a state is much easier than the generation
of a single-qubit state. Therefore our protocols ease Alice's burden.
Furthermore, the security of our protocol is based on the no-signaling
principle, which is more fundamental than quantum physics. Finally, our
protocols are device independent in the sense that Alice does not need to trust
her measurement device in order to guarantee the security.Comment: 9 pages, 3 figure
Power of Quantum Computation with Few Clean Qubits
This paper investigates the power of polynomial-time quantum computation in
which only a very limited number of qubits are initially clean in the |0>
state, and all the remaining qubits are initially in the totally mixed state.
No initializations of qubits are allowed during the computation, nor
intermediate measurements. The main results of this paper are unexpectedly
strong error-reducible properties of such quantum computations. It is proved
that any problem solvable by a polynomial-time quantum computation with
one-sided bounded error that uses logarithmically many clean qubits can also be
solvable with exponentially small one-sided error using just two clean qubits,
and with polynomially small one-sided error using just one clean qubit. It is
further proved in the case of two-sided bounded error that any problem solvable
by such a computation with a constant gap between completeness and soundness
using logarithmically many clean qubits can also be solvable with exponentially
small two-sided error using just two clean qubits. If only one clean qubit is
available, the problem is again still solvable with exponentially small error
in one of the completeness and soundness and polynomially small error in the
other. As an immediate consequence of the above result for the two-sided-error
case, it follows that the TRACE ESTIMATION problem defined with fixed constant
threshold parameters is complete for the classes of problems solvable by
polynomial-time quantum computations with completeness 2/3 and soundness 1/3
using logarithmically many clean qubits and just one clean qubit. The
techniques used for proving the error-reduction results may be of independent
interest in themselves, and one of the technical tools can also be used to show
the hardness of weak classical simulations of one-clean-qubit computations
(i.e., DQC1 computations).Comment: 44 pages + cover page; the results in Section 8 are overlapping with
the main results in arXiv:1409.677
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