20,881 research outputs found
Spinor Fields and Symmetries of the Spacetime
In the background of a stationary black hole, the "conserved current" of a
particular spinor field always approaches the null Killing vector on the
horizon. What's more, when the black hole is asymptotically flat and when the
coordinate system is asymptotically static, then the same current also
approaches the time Killing vector at the spatial infinity. We test these
results against various black hole solutions and no exception is found. The
spinor field only needs to satisfy a very general and simple constraint.Comment: 19 page
Running-phase state in a Josephson washboard potential
We investigate the dynamics of the phase variable of an ideal underdamped
Josephson junction in switching current experiments. These experiments have
provided the first evidence for macroscopic quantum tunneling in large
Josephson junctions and are currently used for state read-out of
superconducting qubits. We calculate the shape of the resulting macroscopic
wavepacket and find that the propagation of the wavepacket long enough after a
switching event leads to an average voltage increasing linearly with time.Comment: 6 pages, 3 figure
Implementing optimal control pulse shaping for improved single-qubit gates
We employ pulse shaping to abate single-qubit gate errors arising from the
weak anharmonicity of transmon superconducting qubits. By applying shaped
pulses to both quadratures of rotation, a phase error induced by the presence
of higher levels is corrected. Using a derivative of the control on the
quadrature channel, we are able to remove the effect of the anharmonic levels
for multiple qubits coupled to a microwave resonator. Randomized benchmarking
is used to quantify the average error per gate, achieving a minimum of
0.007+/-0.005 using 4 ns-wide pulse.Comment: 4 pages, 4 figure
An Exact Conformal Symmetry Ansatz on Kaluza-Klein Reduced TMG
Using a Kaluza-Klein dimensional reduction, and further imposing a conformal
Killing symmetry on the reduced metric generated by the dilaton, we show an
Ansatz that yields many of the known stationary axisymmetric solutions to TMG.Comment: 20 pages, 1 figure, v3: postprint, added one re
Non-local nuclear spin quieting in quantum dot molecules: Optically-induced extended two-electron spin coherence time
We demonstrate the extension of coherence between all four two-electron spin
ground states of an InAs quantum dot molecule (QDM) via non-local suppression
of nuclear spin fluctuations in both constituent quantum dots (QDs), while
optically addressing only the upper QD transitions. Long coherence times are
revealed through dark-state spectroscopy as resulting from nuclear spin locking
mediated by the exchange interaction between the QDs. Lineshape analysis
provides the first measurement of the quieting of the Overhauser field
distribution correlating with reduced nuclear spin fluctuations.Comment: Supplementary materials can be found on the publication page of our
website. http://research.physics.lsa.umich.edu/dst/Publications.htm
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