1,707 research outputs found
N=1 Supersymetric Quantum Mechanics in a Scenario with Lorentz-Symmetry Violation
We show in this paper that the dynamics of a non-relativistic particle with
spin, coupled to an external electromagnetic field and to a background that
breaks Lorentz symmetry, is naturally endowed with an N=1-supersymmetry. This
result is achieved in a superspace approach where the particle coordinates and
the spin degrees of freedom are components of the same supermultiplet.Comment: 6 pages, no figure
Keplerian Squeezed States and Rydberg Wave Packets
We construct minimum-uncertainty solutions of the three-dimensional
Schr\"odinger equation with a Coulomb potential. These wave packets are
localized in radial and angular coordinates and are squeezed states in three
dimensions. They move on elliptical keplerian trajectories and are appropriate
for the description of the corresponding Rydberg wave packets, the production
of which is the focus of current experimental effort. We extend our analysis to
incorporate the effects of quantum defects in alkali-metal atoms, which are
used in experiments.Comment: accepted for publication in Physical Review
A Comment on the Topological Phase for Anti-Particles in a Lorentz-violating environment
Recently, a scheme to analyse topological phases in Quantum Mechanics by
means of the non-relativistic limit of fermions non-minimally coupled to a
Lorentz-breaking background has been proposed. In this letter, we show that the
fixed background, responsible for the Lorentz-symmetry violation, may induce
opposite Aharonov-Casher phases for a particle and its corresponding
antiparticle. We then argue that such a difference may be used to investigate
the asymmetry for particle/anti-particle as well as to propose bounds on the
associated Lorentz-symmetry violating parameters.Comment: 4 pages - A published versio
Fluctuation Superconductivity in Mesoscopic Aluminum Rings
Fluctuations are important near phase transitions, where they can be
difficult to describe quantitatively. Superconductivity in mesoscopic rings is
particularly intriguing because the critical temperature is an oscillatory
function of magnetic field. There is an exact theory for thermal fluctuations
in one-dimensional superconducting rings, which are therefore expected to be an
excellent model system. We measure the susceptibility of many rings, one ring
at a time, using a scanning SQUID that can isolate magnetic signals from seven
orders of magnitude larger background applied flux. We find that the
fluctuation theory describes the results and that a single parameter
characterizes the ways in which the fluctuations are especially important at
magnetic fields where the critical temperature is suppressed.Comment: Reprinted with permission from AAA
Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits
Quantum computers have the potential to solve certain interesting problems
significantly faster than classical computers. To exploit the power of a
quantum computation it is necessary to perform inter-qubit operations and
generate entangled states. Spin qubits are a promising candidate for
implementing a quantum processor due to their potential for scalability and
miniaturization. However, their weak interactions with the environment, which
leads to their long coherence times, makes inter-qubit operations challenging.
We perform a controlled two-qubit operation between singlet-triplet qubits
using a dynamically decoupled sequence that maintains the two-qubit coupling
while decoupling each qubit from its fluctuating environment. Using state
tomography we measure the full density matrix of the system and determine the
concurrence and the fidelity of the generated state, providing proof of
entanglement
Edge-Magnetoplasmon Wave-Packet Revivals in the Quantum Hall Effect
The quantum Hall effect is necessarily accompanied by low-energy excitations
localized at the edge of a two-dimensional electron system. For the case of
electrons interacting via the long-range Coulomb interaction, these excitations
are edge magnetoplasmons. We address the time evolution of localized
edge-magnetoplasmon wave packets. On short times the wave packets move along
the edge with classical E cross B drift. We show that on longer times the wave
packets can have properties similar to those of the Rydberg wave packets that
are produced in atoms using short-pulsed lasers. In particular, we show that
edge-magnetoplasmon wave packets can exhibit periodic revivals in which a
dispersed wave packet reassembles into a localized one. We propose the study of
edge-magnetoplasmon wave packets as a tool to investigate dynamical properties
of integer and fractional quantum-Hall edges. Various scenarios are discussed
for preparing the initial wave packet and for detecting it at a later time. We
comment on the importance of magnetoplasmon-phonon coupling and on quantum and
thermal fluctuations.Comment: 18 pages, RevTex, 7 figures and 2 tables included, Fig. 5 was
originally 3Mbyte and had to be bitmapped for submission to archive; in the
process it acquired distracting artifacts, to upload the better version, see
http://physics.indiana.edu/~uli/publ/projects.htm
Electrometry Using Coherent Exchange Oscillations in a Singlet-Triplet-Qubit
Two level systems that can be reliably controlled and measured hold promise
in both metrology and as qubits for quantum information science (QIS). When
prepared in a superposition of two states and allowed to evolve freely, the
state of the system precesses with a frequency proportional to the splitting
between the states. In QIS,this precession forms the basis for universal
control of the qubit,and in metrology the frequency of the precession provides
a sensitive measurement of the splitting. However, on a timescale of the
coherence time, , the qubit loses its quantum information due to
interactions with its noisy environment, causing qubit oscillations to decay
and setting a limit on the fidelity of quantum control and the precision of
qubit-based measurements. Understanding how the qubit couples to its
environment and the dynamics of the noise in the environment are therefore key
to effective QIS experiments and metrology. Here we show measurements of the
level splitting and dephasing due to voltage noise of a GaAs singlet-triplet
qubit during exchange oscillations. Using free evolution and Hahn echo
experiments we probe the low frequency and high frequency environmental
fluctuations, respectively. The measured fluctuations at high frequencies are
small, allowing the qubit to be used as a charge sensor with a sensitivity of
, two orders of magnitude better than
the quantum limit for an RF single electron transistor (RF-SET). We find that
the dephasing is due to non-Markovian voltage fluctuations in both regimes and
exhibits an unexpected temperature dependence. Based on these measurements we
provide recommendations for improving in future experiments, allowing for
higher fidelity operations and improved charge sensitivity
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