354 research outputs found
Non-Abelian Plane-Waves in the Quark-Gluon Plasma
We present new, non-abelian, solutions to the equations of motion which
describe the collective excitations of a quark-gluon plasma at high
temperature. These solutions correspond to longitudinal and transverse
plane-waves propagating through the plasma.Comment: 13 pages, LaTex, preprint Saclay-T94/01
The Principles of Social Order. Selected Essays of Lon L. Fuller, edited With an introduction by Kenneth I. Winston
The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in 4H-SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10(-6) strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%-36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields
Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point
defects in semiconductors is a key resource for both initializing nuclear
quantum memories and producing nuclear hyperpolarization. DNP is therefore an
important process in the field of quantum-information processing,
sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based
spintronics. DNP based on optical pumping of point defects has been
demonstrated by using the electron spin of nitrogen-vacancy (NV) center in
diamond, and more recently, by using divacancy and related defect spins in
hexagonal silicon carbide (SiC). Here, we describe a general model for these
optical DNP processes that allows the effects of many microscopic processes to
be integrated. Applying this theory, we gain a deeper insight into dynamic
nuclear spin polarization and the physics of diamond and SiC defects. Our
results are in good agreement with experimental observations and provide a
detailed and unified understanding. In particular, our findings show that the
defects' electron spin coherence times and excited state lifetimes are crucial
factors in the entire DNP process
Energy-Momentum Tensors for the Quark-Gluon Plasma
We construct the energy-momentum tensor for the gauge fields which describe
the collective excitations of the quark-gluon plasma. We rely on the
description of the collective modes that we have derived in previous works. By
using the conservation laws for energy and momentum, we obtain three different
versions for the tensor , which are physically equivalent. We show
that the total energy constructed from is positive for any non-trivial
field configuration. Finally, we present a new non-abelian solution of the
equations of motion for the gauge fields. This solution corresponds to
spatially uniform color oscillations of the plasma.Comment: 28 pages LaTex, Saclay preprint T94/0
High fidelity bi-directional nuclear qubit initialization in SiC
Dynamic nuclear polarization (DNP) is an attractive method for initializing
nuclear spins that are strongly coupled to optically active electron spins
because it functions at room temperature and does not require strong magnetic
fields. In this Letter, we demonstrate that DNP, with near-unity polarization
efficiency, can be generally realized in weakly coupled hybrid registers, and
furthermore that the nuclear spin polarization can be completely reversed with
only sub-Gauss magnetic field variations. This mechanism offers new avenues for
DNP-based sensors and radio-frequency free control of nuclear qubits
Soft Collective Excitations in Hot Gauge Theories
THE PREVIOUS LATEX STRUCTURE WAS MODIFIED IN ORDER TO ALLOW FOR A DIRECT
IMPRESSION OF THE PAPER, WITHOUT SUPPLEMENTARY SPLITTING. THERE IS NO TEXT
MODIFICATION.Comment: 67 pages (LaTeX), 8 figures not included (available on request);
report SPhT/93-6
Resolving the positions of defects in superconducting quantum bits
Solid-state quantum coherent devices are quickly progressing. Superconducting circuits, for instance, have already been used to demonstrate prototype quantum processors comprising a few tens of quantum bits. This development also revealed that a major part of decoherence and energy loss in such devices originates from a bath of parasitic material defects. However, neither the microscopic structure of defects nor the mechanisms by which they emerge during sample fabrication are understood. Here, we present a technique to obtain information on locations of defects relative to the thin film edge of the qubit circuit. Resonance frequencies of defects are tuned by exposing the qubit sample to electric fields generated by electrodes surrounding the chip. By determining the defect’s coupling strength to each electrode and comparing it to a simulation of the field distribution, we obtain the probability at which location and at which interface the defect resides. This method is applicable to already existing samples of various qubit types, without further on-chip design changes. It provides a valuable tool for improving the material quality and nano-fabrication procedures towards more coherent quantum circuits
Resolving the positions of defects in superconducting quantum bits
Solid-state quantum coherent devices are quickly progressing. Superconducting
circuits, for instance, have already been used to demonstrate prototype quantum
processors comprising a few tens of quantum bits. This development also
revealed that a major part of decoherence and energy loss in such devices
originates from a bath of parasitic material defects. However, neither the
microscopic structure of defects nor the mechanisms by which they emerge during
sample fabrication are understood. Here, we present a technique to obtain
information on locations of defects relative to the thin film edge of the qubit
circuit. Resonance frequencies of defects are tuned by exposing the qubit
sample to electric fields generated by electrodes surrounding the chip. By
determining the defect's coupling strength to each electrode and comparing it
to a simulation of the field distribution, we obtain the probability at which
location and at which interface the defect resides. This method is applicable
to already existing samples of various qubit types, without further on-chip
design changes. It provides a valuable tool for improving the material quality
and nano-fabrication procedures towards more coherent quantum circuits
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