573 research outputs found
Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System
Quantum simulators, in which well controlled quantum systems are used to
reproduce the dynamics of less understood ones, have the potential to explore
physics that is inaccessible to modeling with classical computers. However,
checking the results of such simulations will also become classically
intractable as system sizes increase. In this work, we introduce and implement
a coherent imaging spectroscopic technique to validate a quantum simulation,
much as magnetic resonance imaging exposes structure in condensed matter. We
use this method to determine the energy levels and interaction strengths of a
fully-connected quantum many-body system. Additionally, we directly measure the
size of the critical energy gap near a quantum phase transition. We expect this
general technique to become an important verification tool for quantum
simulators once experiments advance beyond proof-of-principle demonstrations
and exceed the resources of conventional computers
Quantum Control of Qubits and Atomic Motion Using Ultrafast Laser Pulses
Pulsed lasers offer significant advantages over CW lasers in the coherent
control of qubits. Here we review the theoretical and experimental aspects of
controlling the internal and external states of individual trapped atoms with
pulse trains. Two distinct regimes of laser intensity are identified. When the
pulses are sufficiently weak that the Rabi frequency is much smaller
than the trap frequency \otrap, sideband transitions can be addressed and
atom-atom entanglement can be accomplished in much the same way as with CW
lasers. By contrast, if the pulses are very strong (\Omega \gg \otrap),
impulsive spin-dependent kicks can be combined to create entangling gates which
are much faster than a trap period. These fast entangling gates should work
outside of the Lamb-Dicke regime and be insensitive to thermal atomic motion.Comment: 16 pages, 15 figure
Quantum Catalysis of Magnetic Phase Transitions in a Quantum Simulator
We control quantum fluctuations to create the ground state magnetic phases of
a classical Ising model with a tunable longitudinal magnetic field using a
system of 6 to 10 atomic ion spins. Due to the long-range Ising interactions,
the various ground state spin configurations are separated by multiple
first-order phase transitions, which in our zero temperature system cannot be
driven by thermal fluctuations. We instead use a transverse magnetic field as a
quantum catalyst to observe the first steps of the complete fractal devil's
staircase, which emerges in the thermodynamic limit and can be mapped to a
large number of many-body and energy-optimization problems.Comment: New data in Fig. 3, and much of the paper rewritte
Entanglement of Atomic Qubits using an Optical Frequency Comb
We demonstrate the use of an optical frequency comb to coherently control and
entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used
to efficiently and coherently transfer population between electronic and
vibrational states of trapped atomic ions and implement an entangling quantum
logic gate with high fidelity. This technique can be extended to the high field
regime where operations can be performed faster than the trap frequency. This
general approach can be applied to more complex quantum systems, such as large
collections of interacting atoms or molecules.Comment: 4 pages, 5 figure
Non-thermalization in trapped atomic ion spin chains
Linear arrays of trapped and laser cooled atomic ions are a versatile
platform for studying emergent phenomena in strongly-interacting many-body
systems. Effective spins are encoded in long-lived electronic levels of each
ion and made to interact through laser mediated optical dipole forces. The
advantages of experiments with cold trapped ions, including high spatiotemporal
resolution, decoupling from the external environment, and control over the
system Hamiltonian, are used to measure quantum effects not always accessible
in natural condensed matter samples. In this review we highlight recent work
using trapped ions to explore a variety of non-ergodic phenomena in long-range
interacting spin-models which are heralded by memory of out-of-equilibrium
initial conditions. We observe long-lived memory in static magnetizations for
quenched many-body localization and prethermalization, while memory is
preserved in the periodic oscillations of a driven discrete time crystal state.Comment: 14 pages, 5 figures, submitted for edition of Phil. Trans. R. Soc. A
on "Breakdown of ergodicity in quantum systems
Experimental Realization of a Quantum Integer-Spin Chain with Controllable Interactions
The physics of interacting integer-spin chains has been a topic of intense
theoretical interest, particularly in the context of symmetry-protected
topological phases. However, there has not been a controllable model system to
study this physics experimentally. We demonstrate how spin-dependent forces on
trapped ions can be used to engineer an effective system of interacting spin-1
particles. Our system evolves coherently under an applied spin-1 XY Hamiltonian
with tunable, long-range couplings, and all three quantum levels at each site
participate in the dynamics. We observe the time evolution of the system and
verify its coherence by entangling a pair of effective three-level particles
(`qutrits') with 86% fidelity. By adiabatically ramping a global field, we
produce ground states of the XY model, and we demonstrate an instance where the
ground state cannot be created without breaking the same symmetries that
protect the topological Haldane phase. This experimental platform enables
future studies of symmetry-protected order in spin-1 systems and their use in
quantum applications
Fourier-transform electrospray instrumentation for tandem high-resolution mass spectrometry of large molecules
AbstractMass spectrometry instrumentation providing unit resolution and 10-ppm mass accuracy for molecules larger than 10 kDa was first reported in 1991. This instrumentation has now been improved with a 6.2-T magnet replacing that of 2.8 T, a more efficient vacuum system, ion injection with controlled ion kinetic energies, accumulated ion trapping with an open-cylindrical ion cell, acquisition of 2M data points, and updated electrospray apparatus. The resulting capabilities include resolving power of 5 × 105 for a 29-kDa protein, less than 1-ppm mass measuring error, and dissociation of protein molecular ions to produce dozens of fragment ions whose exact masses can be identified from their mass-to-charge ratio values and isotopic peak spacing
Achievement Goal
Achievement goals are self-regulatory commitments that provide direction to individuals as they interpret and respond to competence-relevant situations. Four types of achievement goals have been the primary focus of the literature: Masteryapproach goals (master a task; improve over time), performance-approach goals (outperform others), mastery-avoidance goals (not fall short of mastering a task; not decline over time), and performance-avoidance goals (not be outperformed by others)
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