28 research outputs found
Superconductivity near Itinerant Ferromagnetic Quantum Criticality
Superconductivity mediated by spin fluctuations in weak and nearly
ferromagnetic metals is studied close to the zero-temperature magnetic
transition. We solve analytically the Eliashberg equations for p-wave pairing
and obtain the normal state quasiparticle self-energy and the superconducting
transition temperature as a function of the distance to the quantum
critical point. We show that the reduction of quasiparticle coherence and
life-time due to scattering by quasistatic spin fluctuations is the dominant
pair-breaking process, which leads to a rapid suppression of to a nonzero
value near the quantum critical point. We point out the differences and the
similarities of the problem to that of the theory of superconductivity in the
presence of paramagnetic impurities.Comment: 4 pages, 1 figure, revised version to appear in Phys. Rev. Let
Quantum Algorithm to Solve Satisfiability Problems
A new quantum algorithm is proposed to solve Satisfiability(SAT) problems by
taking advantage of non-unitary transformation in ground state quantum
computer. The energy gap scale of the ground state quantum computer is analyzed
for 3-bit Exact Cover problems. The time cost of this algorithm on general SAT
problems is discussed.Comment: 5 pages, 3 figure
Quadratic Quantum Measurements
We develop a theory of quadratic quantum measurements by a mesoscopic
detector. It is shown that quadratic measurements should have non-trivial
quantum information properties, providing, for instance, a simple way of
entangling two non-interacting qubits. We also calculate output spectrum of a
quantum detector with both linear and quadratic response continuously
monitoring coherent oscillations in two qubits.Comment: 5 pages, 2 figure
Continuous measurements of two qubits
We develop a theory of coherent quantum oscillations in two, in general
interacting, qubits measured continuously by a mesoscopic detector with
arbitrary non-linearity and discuss an example of SQUID magnetometer that can
operate as such a detector. Calculated spectra of the detector output show that
the detector non-linearity should lead to mixing of the oscillations of the two
qubits. For non-interacting qubits oscillating with frequencies and
, the mixing manifests itself as spectral peaks at the combination
frequencies . Additional nonlinearity introduced by the
qubit-qubit interaction shifts all the frequencies. In particular, for
identical qubits, the interaction splits coherent superposition of the
single-qubit peaks at . Quantum mechanics of the measurement
imposes limitations on the height of the spectral peaks.Comment: 14 pages, 6 figure
Thermoelectric Figure of Merit of Strongly Correlated Superlattice Semiconductors
We solved the Anderson Lattice Hamiltonian to get the energy bands of a
strongly correlated semiconductor by using slave boson mean field theory. The
transport properties were calculated in the relaxation-time approximation,and
the thermoelectric figure of merit was obtained for the strongly correlated
semiconductor and its superlattice structures. We found that at room
temperature can reach nearly 2 for the quantum wire lattice structure.We
believe that it is possible to find high values of thermoelectric figure of
merit from strongly correlated semiconductor superlattice systems.Comment: 4 pages, 3 figure
A Two-Dimensional Model with Chiral Condensates and Cooper Pairs Having QCD-like Phase Structure
We describe how a generalization of the original Gross-Neveu model from U(N)
to O(N) flavor symmetry leads to the appearance of a pairing condensate at high
density, in agreement with the conjectured phenomenon of color
superconductivity in -dimensional QCD. Moreover, the model displays a
rich phase structure which closely resembles the one expected in two-flavor
QCD.Comment: 11 pages, 1 fugure, Presented at TMU-Yale Symposium on Dynamics of
Gauge Fields: An External Activity of APCTP, Tokyo, Japan, 13-15 Dec 199
Equilibrium and nonequilibrium properties associated with the chiral phase transition at finite density in the Gross-Neveu Model
We study the dynamics of the chiral phase transition at finite density in the
Gross-Neveu (GN) model in the leading order in large-N approximation. The phase
structure of the GN model in this approximation has the property that there is
a tricritical point at a fixed temperature and chemical potential separating
regions where the chiral transition is first order from that where it is second
order. We consider evolutions starting in local thermal and chemical
equilibrium in the massless unbroken phase for conditions pertaining to
traversing a first or second order phase transition. We assume boost invariant
kinematics and determine the evolution of the order parameter , the
energy density and pressure as well as the effective temperature, chemical
potential and interpolating number densities as a function of the proper time
. We find that before the phase transition, the system behaves as if it
were an ideal fluid in local thermal equilibrium with equation of state
. After the phase transition, the system quickly reaches its true
broken symmetry vacuum value for the fermion mass and for the energy density.
The single particle distribution functions for Fermions and anti-Fermions go
far out of equilibrium as soon as the plasma traverses the chiral phase
transition. We have also determined the spatial dependence of the "pion"
Green's function as a function of the proper time.Comment: 39 pages, 23 figure