67 research outputs found
Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor
We present the first demonstration of vortices in an electron-type cuprate
superconductor, the highest (= 43 K) electron-type cuprate
. Our spatially resolved quasiparticle tunneling spectra
reveal a hidden low-energy pseudogap inside the vortex core and unconventional
spectral evolution with temperature and magnetic field. These results cannot be
easily explained by the scenario of pure superconductivity in the ground state
of high- superconductivity.Comment: 6 pages, 4 figures. Two new graphs have been added into Figure 2.
Accepted for publication in Europhysics Letters. Corresponding author:
Nai-Chang Yeh (E-mail: [email protected]
Four-dimensional ultrafast electron microscopy of phase transitions
Reported here is direct imaging (and diffraction) by using 4D ultrafast electron microscopy (UEM) with combined spatial and temporal resolutions. In the first phase of UEM, it was possible to obtain snapshot images by using timed, single-electron packets; each packet is free of space–charge effects. Here, we demonstrate the ability to obtain sequences of snapshots ("movies") with atomic-scale spatial resolution and ultrashort temporal resolution. Specifically, it is shown that ultrafast metal–insulator phase transitions can be studied with these achieved spatial and temporal resolutions. The diffraction (atomic scale) and images (nanometer scale) we obtained manifest the structural phase transition with its characteristic hysteresis, and the time scale involved (100 fs) is now studied by directly monitoring coordinates of the atoms themselves
The Loschmidt Echo as a robust decoherence quantifier for many-body systems
We employ the Loschmidt Echo, i.e. the signal recovered after the reversal of
an evolution, to identify and quantify the processes contributing to
decoherence. This procedure, which has been extensively used in single particle
physics, is here employed in a spin ladder. The isolated chains have 1/2 spins
with XY interaction and their excitations would sustain a one-body like
propagation. One of them constitutes the controlled system S whose reversible
dynamics is degraded by the weak coupling with the uncontrolled second chain,
i.e. the environment E. The perturbative SE coupling is swept through arbitrary
combinations of XY and Ising like interactions, that contain the standard
Heisenberg and dipolar ones. Different time regimes are identified for the
Loschmidt Echo dynamics in this perturbative configuration. In particular, the
exponential decay scales as a Fermi golden rule, where the contributions of the
different SE terms are individually evaluated and analyzed. Comparisons with
previous analytical and numerical evaluations of decoherence based on the
attenuation of specific interferences, show that the Loschmidt Echo is an
advantageous decoherence quantifier at any time, regardless of the S internal
dynamics.Comment: 12 pages, 6 figure
Coherent, mechanical control of a single electronic spin
The ability to control and manipulate spins via electrical, magnetic and
optical means has generated numerous applications in metrology and quantum
information science in recent years. A promising alternative method for spin
manipulation is the use of mechanical motion, where the oscillation of a
mechanical resonator can be magnetically coupled to a spins magnetic dipole,
which could enable scalable quantum information architectures9 and sensitive
nanoscale magnetometry. To date, however, only population control of spins has
been realized via classical motion of a mechanical resonator. Here, we
demonstrate coherent mechanical control of an individual spin under ambient
conditions using the driven motion of a mechanical resonator that is
magnetically coupled to the electronic spin of a single nitrogen-vacancy (NV)
color center in diamond. Coherent control of this hybrid mechanical/spin system
is achieved by synchronizing pulsed spin-addressing protocols (involving
optical and radiofrequency fields) to the motion of the driven oscillator,
which allows coherent mechanical manipulation of both the population and phase
of the spin via motion-induced Zeeman shifts of the NV spins energy. We
demonstrate applications of this coherent mechanical spin-control technique to
sensitive nanoscale scanning magnetometry.Comment: 6 pages, 4 figure
Scanning tunneling spectroscopic evidence for magnetic field-induced microscopic orders in the high- superconductor YBaCuO
We report spatially resolved tunneling spectroscopic evidence for
field-induced microscopic orders in a high- superconductor . The spectral characteristics inside vortices reveal a
pseudogap () larger than the superconducting gap () as well as a subgap () smaller than ,
and the spectral weight shifts steadily from to
and upon increasing magnetic field. Additionally,
energy-independent conductance modulations at 3.6 and 7.1 lattice constants
along the Cu-O bonding directions and at 9.5 lattice constants along the nodal
directions are manifested in the vortex state. These wave-vectors differ
fundamentally from the strongly dispersive modes due to Bogoliubov
quasiparticle scattering interferences and may be associated with field-induced
microscopic orders of pair-, charge- and spin-density waves.Comment: Paper updated and accepted for publication in Europhysics Letters. 4
figures and 6 pages. Corresponding author: Nai-Chang Yeh (E-mail:
[email protected]
A robust, scanning quantum system for nanoscale sensing and imaging
Controllable atomic-scale quantum systems hold great potential as sensitive
tools for nanoscale imaging and metrology. Possible applications range from
nanoscale electric and magnetic field sensing to single photon microscopy,
quantum information processing, and bioimaging. At the heart of such schemes is
the ability to scan and accurately position a robust sensor within a few
nanometers of a sample of interest, while preserving the sensor's quantum
coherence and readout fidelity. These combined requirements remain a challenge
for all existing approaches that rely on direct grafting of individual solid
state quantum systems or single molecules onto scanning-probe tips. Here, we
demonstrate the fabrication and room temperature operation of a robust and
isolated atomic-scale quantum sensor for scanning probe microscopy.
Specifically, we employ a high-purity, single-crystalline diamond nanopillar
probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the
versatility and performance of our scanning NV sensor by conducting
quantitative nanoscale magnetic field imaging and near-field single-photon
fluorescence quenching microscopy. In both cases, we obtain imaging resolution
in the range of 20 nm and sensitivity unprecedented in scanning quantum probe
microscopy
Quantum control of proximal spins using nanoscale magnetic resonance imaging
Quantum control of individual spins in condensed matter systems is an
emerging field with wide-ranging applications in spintronics, quantum
computation, and sensitive magnetometry. Recent experiments have demonstrated
the ability to address and manipulate single electron spins through either
optical or electrical techniques. However, it is a challenge to extend
individual spin control to nanoscale multi-electron systems, as individual
spins are often irresolvable with existing methods. Here we demonstrate that
coherent individual spin control can be achieved with few-nm resolution for
proximal electron spins by performing single-spin magnetic resonance imaging
(MRI), which is realized via a scanning magnetic field gradient that is both
strong enough to achieve nanometric spatial resolution and sufficiently stable
for coherent spin manipulations. We apply this scanning field-gradient MRI
technique to electronic spins in nitrogen-vacancy (NV) centers in diamond and
achieve nanometric resolution in imaging, characterization, and manipulation of
individual spins. For NV centers, our results in individual spin control
demonstrate an improvement of nearly two orders of magnitude in spatial
resolution compared to conventional optical diffraction-limited techniques.
This scanning-field-gradient microscope enables a wide range of applications
including materials characterization, spin entanglement, and nanoscale
magnetometry.Comment: 7 pages, 4 figure
Composite-pulse magnetometry with a solid-state quantum sensor
The sensitivity of quantum magnetometers is challenged by control errors and,
especially in the solid-state, by their short coherence times. Refocusing
techniques can overcome these limitations and improve the sensitivity to
periodic fields, but they come at the cost of reduced bandwidth and cannot be
applied to sense static (DC) or aperiodic fields. Here we experimentally
demonstrate that continuous driving of the sensor spin by a composite pulse
known as rotary-echo (RE) yields a flexible magnetometry scheme, mitigating
both driving power imperfections and decoherence. A suitable choice of RE
parameters compensates for different scenarios of noise strength and origin.
The method can be applied to nanoscale sensing in variable environments or to
realize noise spectroscopy. In a room-temperature implementation based on a
single electronic spin in diamond, composite-pulse magnetometry provides a
tunable trade-off between sensitivities in the microT/sqrt(Hz) range,
comparable to those obtained with Ramsey spectroscopy, and coherence times
approaching T1
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