675 research outputs found
Towards phase-coherent caloritronics in superconducting circuits
The emerging field of phase-coherent caloritronics (from the Latin word
"calor", i.e., heat) is based on the possibility to control heat currents using
the phase difference of the superconducting order parameter. The goal is to
design and implement thermal devices able to master energy transfer with a
degree of accuracy approaching the one reached for charge transport by
contemporary electronic components. This can be obtained by exploiting the
macroscopic quantum coherence intrinsic to superconducting condensates, which
manifests itself through the Josephson and the proximity effect. Here, we
review recent experimental results obtained in the realization of heat
interferometers and thermal rectifiers, and discuss a few proposals for exotic
non-linear phase-coherent caloritronic devices, such as thermal transistors,
solid-state memories, phase-coherent heat splitters, microwave refrigerators,
thermal engines and heat valves. Besides being very attractive from the
fundamental physics point of view, these systems are expected to have a vast
impact on many cryogenic microcircuits requiring energy management, and
possibly lay the first stone for the foundation of electronic thermal logic.Comment: 11 pages, 6 colour figure
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
Multiphoton transitions in Josephson-junction qubits (Review Article)
Two basic physical models, a two-level system and a harmonic oscillator, are
realized on the mesoscopic scale as coupled qubit and resonator. The realistic
system includes moreover the electronics for controlling the distance between
the qubit energy levels and their populations and to read out the resonator's
state, as well as the unavoidable dissipative environment. Such rich system is
interesting both for the study of fundamental quantum phenomena on the
mesoscopic scale and as a promising system for future electronic devices. We
present recent results for the driven superconducting qubit-resonator system,
where the resonator can be realized as an LC circuit or a nanomechanical
resonator. Most of the results can be described by the semiclassical theory,
where a qubit is treated as a quantum two-level system coupled to the classical
driving field and the classical resonator. Application of this theory allows to
describe many phenomena for the single and two coupled superconducting qubits,
among which are the following: the equilibrium-state and weak-driving
spectroscopy, Sisyphus damping and amplification, Landau-Zener-St\"uckelberg
interferometry, the multiphoton transitions of both direct and ladder- type
character, and creation of the inverse population for lasing.Comment: 20 pages, 15 figure
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