133 research outputs found
Thermodynamic fingerprints of non-Markovianity in a system of coupled superconducting qubits
The exploitation and characterization of memory effects arising from the
interaction between system and environment is a key prerequisite for quantum
reservoir engineering beyond the standard Markovian limit. In this paper we
investigate a prototype of non-Markovian dynamics experimentally implementable
with superconducting qubits. We rigorously quantify non-Markovianity
highlighting the effects of the environmental temperature on the Markovian to
non-Markovian crossover. We investigate how memory effects influence, and
specifically suppress, the ability to perform work on the driven qubit. We show
that the average work performed on the qubit can be used as a diagnostic tool
to detect the presence or absence of memory effects.Comment: 9 page
Measurement of coherent charge transfer in an adiabatic Cooper pair pump
We study adiabatic charge transfer in a superconducting Cooper pair pump,
focusing on the influence of current measurement on coherence. We investigate
the limit where the Josephson coupling energy between the various parts
of the system is small compared to the Coulomb charging energy . In this
case the charge transferred in a pumping cycle , the charge of one
Cooper pair: the main contribution is due to incoherent Cooper pair tunneling.
We are particularly interested in the quantum correction to , which is due
to coherent tunneling of pairs across the pump and which depends on the
superconducting phase difference between the electrodes: . A measurement of tends to destroy the phase
coherence. We first study an arbitrary measuring circuit and then specific
examples and show that coherent Cooper pair transfer can in principle be
detected using an inductively shunted ammeter
Normal metal - superconductor tunnel junction as a Brownian refrigerator
Thermal noise generated by a hot resistor (resistance ) can, under proper
conditions, catalyze heat removal from a cold normal metal (N) in contact with
a superconductor (S) via a tunnel barrier. Such a NIS junction acts as
Maxwell's demon, rectifying the heat flow. Upon reversal of the temperature
gradient between the resistor and the junction the heat fluxes are reversed:
this presents a regime which is not accessible in an ordinary voltage-biased
NIS structure. We obtain analytical results for the cooling performance in an
idealized high impedance environment, and perform numerical calculations for
general . We conclude by assessing the experimental feasibility of the
proposed effect
Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces
We characterize niobium-based lateral Superconductor (S) - Normal metal (N) -
Superconductor weak links through low-temperature switching current
measurements and tunnel spectroscopy. We fabricate the SNS devices in two
separate lithography and deposition steps, combined with strong argon ion
cleaning before the normal metal deposition in the last step. Our SNS weak link
consists of high-quality sputtered Nb electrodes that are contacted with
evaporated Cu. The two-step fabrication flow enables great flexibility in the
choice of materials and pattern design. A comparison of the
temperature-dependent equilibrium critical supercurrent with theoretical
predictions indicates that the quality of the Nb-Cu interface is similar to
that of evaporated Al-Cu weak links. Aiming at increased sensitivity, range of
operation temperatures, and thermal isolation, we investigate how these SNS
structures can be combined with shadow-evaporated aluminum tunnel junctions for
sensor applications that utilize the superconducting proximity effect. To this
end, we demonstrate a hybrid magnetic flux sensor based on a Nb-Cu-Nb SNS
junction, where the phase-dependent normal metal density of states is probed
with an Al tunnel junction.Comment: 5 pages, 3 figure
Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK
The Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid 3He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear-orientation temperature scale. The superfluid transition temperature (Tc) of 3He at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. Tc on the NBS scale was found to be 1.025 ± 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of 3He.Peer reviewe
Persistent-Current Experiments on Superfluid 3He-B and 3He-A
We have investigated persistent flow of superfluid 3He with an ac gyroscope filled with 20-μm powder. In 3He-B, currents circulate undiminished for 48 h at least; this implies a viscosity 12 orders of magnitude lower than in the normal fluid. In 3He-A, the current does not persist. The observed critical velocity in 3He-B at P12 bars there are two regimes in the B phase: For example, at 29.3 bars the ultimate critical velocities are 5.4 and 7.8 mm/s, respectively.Peer reviewe
Critical current of He3-A in narrow channels
The critical current Jc of superfluid He3-A in 0.8-μm-diam channels has been measured by the observation of the pressure difference along the channels versus the mass current. During warming Jc was found to decrease by about 30% at TBA(cyl) and by another 30% at TBA; TBA(cyl) is the reduced B→A transition temperature in the narrow flow channels, with TBA(cyl)TBA=0.92 at 27.4 bars. Above TBA a second dissipative mechanism was observed at lower currents. These features are believed to be associated with the ends of the channels. © 1982 The American Physical Society
Fluctuation superconductivity limited noise in a transition-edge sensor
In order to investigate the origin of the until now unaccounted excess noise
and to minimize the uncontrollable phenomena at the transition in X-ray
microcalorimeters we have developed superconducting transition-edge sensors
into an edgeless geometry, the so-called Corbino disk (CorTES), with
superconducting contacts in the centre and at the outer perimeter. The measured
rms current noise and its spectral density can be modeled as resistance noise
resulting from fluctuations near the equilibrium superconductor-normal metal
boundaryComment: 9 pages, 4 figures.; Corrections to text and equations; replaced the
affected figures. Added reference [12
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