94 research outputs found
Chirality waves in two-dimensional magnets
We theoretically show that moderate interaction between electrons confined to
move in a plane and localized magnetic moments leads to formation of a
noncoplanar magnetic state. The state is similar to the skyrmion crystal
recently observed in cubic systems with the Dzyaloshinskii-Moriya interaction;
however, it does not require spin-orbit interaction. The non-coplanar magnetism
is accompanied by the ground-state electrical and spin currents, generated via
the real-space Berry phase mechanism. We examine the stability of the state
with respect to lattice discreteness effects and the magnitude of magnetic
exchange interaction. The state can be realized in a number of transition metal
and magnetic semiconductor systems
Coherent macroscopic quantum tunneling in boson-fermion mixtures
We show that the cold atom systems of simultaneously trapped Bose-Einstein
condensates (BEC's) and quantum degenerate fermionic atoms provide promising
laboratories for the study of macroscopic quantum tunneling. Our theoretical
studies reveal that the spatial extent of a small trapped BEC immersed in a
Fermi sea can tunnel and coherently oscillate between the values of the
separated and mixed configurations (the phases of the phase separation
transition of BEC-fermion systems). We evaluate the period, amplitude and
dissipation rate for Na and K-atoms and we discuss the
experimental prospects for observing this phenomenon.Comment: 4 pages, 3 figure
Relaxation and Zeno effect in qubit measurements
We consider a qubit interacting with its environment and continuously
monitored by a detector represented by a point contact. Bloch-type equations
describing the entire system of the qubit, the environment and the detector are
derived. Using these equations we evaluate the detector current and its noise
spectrum in terms of the decoherence and relaxation rates of the qubit. Simple
expressions are obtained that show how these quantities can be accurately
measured. We demonstrate that due to interaction with the environment, the
measurement can never localize a qubit even for infinite decoherence rate.Comment: some clarifications added, to appear in Phys. Rev. Let
Efficiency of thin film photocells
We propose a new concept for the design of high-efficiency photocells based
on ultra-thin (submicron) semiconductor films of controlled thickness. Using a
microscopic model of a thin dielectric layer interacting with incident
electromagnetic radiation we evaluate the efficiency of conversion of solar
radiation into the electric power. We determine the optimal range of parameters
which maximize the efficiency of such photovoltaic element.Comment: 5 pages, 3 figure
Quantum computing with spin qubits in semiconductor structures
We survey recent work on designing and evaluating quantum computing
implementations based on nuclear or bound-electron spins in semiconductor
heterostructures at low temperatures and in high magnetic fields. General
overview is followed by a summary of results of our theoretical calculations of
decoherence time scales and spin-spin interactions. The latter were carried out
for systems for which the two-dimensional electron gas provides the dominant
carrier for spin dynamics via exchange of spin-excitons in the integer quantum
Hall regime.Comment: 18 pages in PD
- …