53 research outputs found
Sensitivity and Linearity of Superconducting Radio-Frequency Single-Electron Transistors: Effects of Quantum Charge Fluctuations
We have investigated the effects of quantum fluctuations of quasiparticles on
the operation of superconducting radio-frequency single-electron transistors
(RF-SETs) for large values of the quasiparticle cotunneling parameter
, where and are the Josephson and charging
energies. We find that for , subgap RF-SET operation is still
feasible despite quantum fluctuations that renormalize the SET charging energy
and wash out quasiparticle tunneling thresholds. Surprisingly, such RF-SETs
show linearity and signal-to-noise ratio superior to those obtained when
quantum fluctuations are weak, while still demonstrating excellent charge
sensitivity.Comment: Submitted to Phys. Rev. Let
Iterative solutions to the steady state density matrix for optomechanical systems
We present a sparse matrix permutation from graph theory that gives stable
incomplete Lower-Upper (LU) preconditioners necessary for iterative solutions
to the steady state density matrix for quantum optomechanical systems. This
reordering is efficient, adding little overhead to the computation, and results
in a marked reduction in both memory and runtime requirements compared to other
solution methods, with performance gains increasing with system size. Either of
these benchmarks can be tuned via the preconditioner accuracy and solution
tolerance. This reordering optimizes the condition number of the approximate
inverse, and is the only method found to be stable at large Hilbert space
dimensions. This allows for steady state solutions to otherwise intractable
quantum optomechanical systems.Comment: 10 pages, 5 figure
Universal quantum fluctuations of a cavity mode driven by a Josephson junction
We analyze the quantum dynamics of a superconducting cavity coupled to a
voltage biased Josephson junction. The cavity is strongly excited at resonances
where the voltage energy lost by a Cooper pair traversing the circuit is a
multiple of the cavity photon energy. We find that the resonances are
accompanied by substantial squeezing of the quantum fluctuations of the cavity
over a broad range of parameters and are able to identify regimes where the
fluctuations in the system take on universal values.Comment: 5 pages, 4 figure
Signatures of Valley Kondo Effect in Si/SiGe Quantum Dots
We report measurements consistent with the valley Kondo effect in Si/SiGe
quantum dots, evidenced by peaks in the conductance versus source-drain voltage
that show strong temperature dependence. The Kondo peaks show unusual behavior
in a magnetic field that we interpret as arising from the valley degree of
freedom. The interplay of valley and Zeeman splittings is suggested by the
presence of side peaks, revealing a zero-field valley splitting between 0.28 to
0.34 meV. A zero-bias conductance peak for non-zero magnetic field, a
phenomenon consistent with valley non- conservation in tunneling, is observed
in two samples.Comment: 16 pages, 7 figure
On-Chip Matching Networks for Radio-Frequency Single-Electron-Transistors
In this letter, we describe operation of a radio-frequency superconducting
single electron transistor (RF-SSET) with an on-chip superconducting LC
matching network consisting of a spiral inductor L and its capacitance to
ground. The superconducting network has a lower parasitic capacitance and gives
a better matching for the RF-SSET than does a commercial chip inductor.
Moreover, the superconducting network has negligibly low dissipation, leading
to sensitive response to changes in the RF-SSET impedance. The charge
sensitivity 2.4*10^-6 e/(Hz)^1/2 in the sub-gap region and energy sensitivity
of 1.9 hbar indicate that the RF-SSET is operating in the vicinity of the shot
noise limit.Comment: 3 pages, 3 figures, REVTeX 4. To appear in Appl. Phys. Let
Si/SiGe quantum dot with superconducting single-electron transistor charge sensor
We report a robust process for fabrication of surface-gated Si/SiGe quantum
dots (QDs) with an integrated superconducting single-electron transistor
(S-SET) charge sensor. A combination of a deep mesa etch and AlOx backfill is
used to reduce gate leakage. After the leakage current is suppressed, Coulomb
oscillations of the QD and the current-voltage characteristics of the S-SET are
observed at a temperature of 0.3 K. Coupling of the S-SET to the QD is
confirmed by using the S-SET to perform sensing of the QD charge state.Comment: 4 pages, 3 figure
Analogue Hawking Radiation in a dc-SQUID Array Transmission Line
We propose the use of a superconducting transmission line formed from an array of dc-SQUID’s for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with an horizon. Being a fundamentally quantum mechanical device, this setup allows for investigations of quantum effects such as back-reaction and analogue space-time fluctuations on the Hawking process
Charge Transport Processes in a Superconducting Single-Electron Transistor Coupled to a Microstrip Transmission Line
We have investigated charge transport processes in a superconducting
single-electron transistor (S-SET) fabricated in close proximity to a
two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. The
macroscopic bonding pads of the S-SET along with the 2DEG form a microstrip
transmission line. We observe a variety of current-carrying cycles in the S-SET
which we attribute to simultaneous tunneling of Cooper pairs and emission of
photons into the microstrip. We find good agreement between these experimental
results and simulations including both photon emission and photon-assisted
tunneling due to the electromagnetic environment.Comment: 4 pages, 4 figures, REVTeX
Hall Conductivity near the z=2 Superconductor-Insulator Transition in 2D
We analyze here the behavior of the Hall conductivity near a
insulator-superconductor quantum critical point in a perpendicular
magnetic field. We show that the form of the conductivity is sensitive to the
presence of dissipation , and depends non-monotonically on once
is weak enough. passes through a maximum at in the quantum critical regime, suggesting that the limits and
do not commute.Comment: 4 pages, 1 .eps figure, to appear in Phys. Rev.
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