3,697 research outputs found
Optical drive of macroscopic mechanical motion by a single two-level system
A quantum emitter coupled to a nano-mechanical oscillator is a hybrid system
where a macroscopic degree of freedom is coupled to a purely quantum system.
Recent progress in nanotechnology has led to the realization of such devices by
embedding single artificial atoms like quantum dots or superconducting qubits
into vibrating wires or membranes, opening up new perspectives for quantum
information technologies and for the exploration of the quantum-classical
boundary. In this letter, we show that the quantum emitter can be turned into a
strikingly efficient light-controlled source of mechanical power, by exploiting
constructive interferences of classical phonon fields in the mechanical
oscillator. We show that this mechanism can be used as a novel strategy to
carry out low-background non-destructive single-shot measurement of an
optically active quantum bit state.Comment: 8 pages, 5 figure
Phonon mediated conversion of exciton-polaritons Rabi oscillation into THz radiation
Semiconductor microcavities in the strong-coupling regime exhibit an energy
scale in the THz frequency range, which is fixed by the Rabi splitting between
the upper and lower exciton-polariton states. While this range can be tuned by
several orders of magnitude using different excitonic medium, the transition
between both polaritonic states is dipole forbidden. In this work we show that
in Cadmium Telluride microcavities, the Rabi-oscillation driven THz radiation
is actually active without the need for any change in the microcavity design.
This feature results from the unique resonance condition which is achieved
between the Rabi splitting and the phonon-polariton states, and leads to a
giant enhancement of the second order nonlinearity.Comment: 6 pages, 2 figure
Thermal decoherence of a nonequilibrium polariton fluid
Exciton-polaritons constitute a unique realization of a quantum fluid
interacting with its environment. Using Selenide based microcavities, we
exploit this feature to warm up a polariton condensate in a controlled way and
monitor its spatial coherence. We determine directly the amount of heat picked
up by the condensate by measuring the phonon-polariton scattering rate and
comparing it with the loss rate. We find that upon increasing the heating rate,
the spatial coherence length decreases markedly, while localized phase
structures vanish, in good agreement with a stochastic mean field theory. From
the thermodynamical point-of-view, this regime is unique as it involves a
nonequilibrium quantum fluid with no well-defined temperature, but which is
nevertheless able to pick up heat with dramatic effects on the order parameter.Comment: 6 pages, 4 figure
Long range correlations in a 97% excitonic one-dimensional polariton condensate
We report on the realization of an out-of-equilibrium polariton condensate
under pulsed excitation in a one-dimensional geometry. We observe macroscopic
occupation of a polaritonic mode with only 3% photonic fraction, and a nature
strikingly close to that of a bare exciton condensate. With the help of this
tiny photonic fraction, the condensate is found to display first-order
coherence over distances as large as 10 microns. Based on a driven-dissipative
mean field model, we find that the correlations length is limited by the
effects of a shallow disorder under non-equilibrium conditions.Comment: 5 pages, 3 figure
Reversible work extraction in a hybrid opto-mechanical system
With the progress of nano-technology, thermodynamics also has to be scaled
down, calling for specific protocols to extract and measure work. Usually, such
protocols involve the action of an external, classical field (the battery) of
infinite energy, that controls the energy levels of a small quantum system (the
calorific fluid). Here we suggest a realistic device to reversibly extract work
in a battery of finite energy : a hybrid optomechanical system. Such devices
consist in an optically active two-level quantum system interacting strongly
with a nano-mechanical oscillator that provides and stores mechanical work,
playing the role of the battery. We identify protocols where the battery
exchanges large, measurable amounts of work with the quantum emitter without
getting entangled with it. When the quantum emitter is coupled to a thermal
bath, we show that thermodynamic reversibility is attainable with
state-of-the-art devices, paving the road towards the realization of a full
cycle of information-to-energy conversion at the single bit level.Comment: 10 pages, 3 figure
Bose Polaron in a quantum fluid of light
We study the Bose polaron problem in a nonequilibrium setting, by considering
an impurity embedded in a quantum fluid of light realized by exciton-polaritons
in a microcavity, subject to a coherent drive and dissipation on account of
pump and cavity losses. We obtain the polaron effective mass, the drag force
acting on the impurity, and determine polaron trajectories at a semiclassical
level. We find different dynamical regimes, originating from the unique
features of the excitation spectrum of driven-dissipative polariton fluids, in
particular a non-trivial regime of acceleration against the flow. Our work
promotes the study of impurity dynamics as an alternative testbed for probing
superfluidity in quantum fluids of light.Comment: Submitted to SciPost Physics; corrected typos, added references,
results are unchange
Mapping the history of public economics in the twentieth century: an introduction to the special issue
The papers in this issue deal with the transformation from public finance to public economics at a theoretical and philosophical level in the mid-twentieth century. Our introduction situates these papers within their intellectual context. To do so, we provide a broad outline of the trajectory of the field beginning with the transformation of welfare economics. Acknowledging the structuring role of Richard Musgrave and James Buchanan for the field, the papers highlight the key role also played by Paul Samuelson in the transition to public economics. Moreover, they underscore how ethical issues were formalised into normative economics at this critical juncture
From public finance to public economics
The emergence of the expression of ‘public economics’ marked an epistemological rupture in the economic discourse about the state. The local problems and national intellectual traditions that had shaped the centuries-old field of public finance were cast aside in favour of new problems and new methods. From the 1970s onward, public economics became an integrated international field defined by a methodological approach embodied in general equilibrium. Mathematics and optimisation changed the nature of the questions considered. After briefly outlining the historic constitution of the field of public finance and how it was transformed in the middle of the twentieth century, we explain how a new economic theory of public expenditures emerged with one foot in the old public finance and one foot in the new public economics. We then hint at how the integration of risk into economic theory unexpectedly transformed the way economists conceptualised the public sector. Last, we consider how the maximisation of social welfare functions exhibiting a trade-off between equity and efficiency replaced principles of taxation
Dispersion relation of the collective excitations in a resonantly driven polariton fluid
Exciton-polaritons in semiconductor microcavities constitute the archetypal
realization of a quantum fluid of light. Under coherent optical drive,
remarkable effects such as superfluidity, dark solitons or the nucleation of
hydrodynamic vortices have been observed. These phenomena can be all understood
as a specific manifestation of collective excitations forming on top of the
polariton condensate. In this work, we performed a Brillouin scattering
experiment to measure their dispersion relation directly.
The result, such as a speed of sound which is apparently twice too low, cannot
be explained upon considering the polariton condensate alone. In a combined
theoretical and experimental analysis, we demonstrate that the presence of a
reservoir of long-lived excitons interacting with polaritons has a dramatic
influence on the nature and characteristic of the quantum fluid, and that it
explains our measurement quantitatively. This work clarifies the role of such a
reservoir in the different polariton hydrodynamics phenomena occurring under
resonant optical drive. It also provides an unambiguous tool to determine the
condensate-to-reservoir fraction in the quantum fluid, and sets an accurate
framework to approach novel ideas for polariton-based quantum-optical
applications
Galilean boosts and superfluidity of resonantly driven polariton fluids in the presence of an incoherent reservoir
We theoretically investigate how the presence of a reservoir of incoherent
excitations affects the superfluidity properties of resonantly driven polariton
fluids. While in the absence of reservoir the two cases of a defect moving in a
fluid at rest and of a fluid flowing against a static defect are linked by a
formal Galilean transformation, here the reservoir defines a privileged
reference frame attached to the semiconductor structure and causes markedly
different features between the two settings. The consequences on the critical
velocity for superfluidity are highlighted and compared to experiments in
resonantly driven excitons polaritons.Comment: 13 pages, 7 figure
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