12 research outputs found
Electron-phonon decoupling due to strong light-matter interactions
Phonon interactions in solid-state photonics systems cause intrinsic quantum
decoherence and often present the limiting factor in emerging quantum
technology. Due to recent developments in nanophotonics, exciton-cavity
structures with very strong light-matter coupling rates can be fabricated. We
show that in such structures, a new regime emerges, where the decoherence is
completely suppressed due to decoupling of the dominant phonon process. Using a
numerically exact tensor network approach, we perform calculations in this
non-perturbative, non-Markovian dynamical regime. Here, we identify a strategy
for reaching near-unity photon indistinguishability and also discover an
interesting phonon-dressing of the exciton-cavity polaritons in the high-Q
regime, leading to multiple phonon sidebands when the light-matter interaction
is sufficiently strong.Comment: Accepted for publication in Physical Review
Dynamics and condensation of polaritons in an optical nanocavity coupled to two-dimensional materials
We present a comprehensive investigation of the light-matter interaction
dynamics in two-dimensional materials coupled with a spectrally isolated cavity
mode in the strong coupling regime. The interaction between light and matter
breaks the translational symmetry of excitons in the two-dimensional lattice
and results in the emergence of a localized polariton state. Employing a novel
approach involving transformation to exciton reaction coordinates, we derive a
Markovian master equation to describe the formation of a macroscopic population
in the localized polariton state. Our study shows that the construction of a
large-scale polariton population is affected by correction terms addressing the
breakdown of translational symmetry. Increasing the spatial width of the cavity
mode increases the Coulomb scattering rates while the correction terms saturate
and affect the system's dynamics progressively less. Tuning the lattice
temperature can induce bistability and hysteresis with different origins than
those recognized for quantum wells in larger microcavities. We identify a limit
temperature as a key factor for stimulated emissions and
forming a macroscopic population, enriching our understanding of strong
coupling dynamics in systems with extreme confinement.Comment: 15 pages, 15 figure
Protocol for generating multiphoton entangled states from quantum dots in the presence of nuclear spin fluctuations
Multi-photon entangled states are a crucial resource for many applications in
quantum information science. Semiconductor quantum dots offer a promising route
to generate such states by mediating photon-photon correlations via a confined
electron spin, but dephasing caused by the host nuclear spin environment
typically limits coherence (and hence entanglement) between photons to the spin
time of a few nanoseconds. We propose a protocol for the deterministic
generation of multi-photon entangled states that is inherently robust against
the dominating slow nuclear spin environment fluctuations, meaning that
coherence and entanglement is instead limited only by the much longer spin
time of microseconds. Unlike previous protocols, the present scheme
allows for the generation of very low error probability polarisation encoded
three-photon GHZ states and larger entangled states, without the need for spin
echo or nuclear spin calming techniques
Collective Quantum Memory Activated by a Driven Central Spin
Coupling a qubit coherently to an ensemble is the basis for collective quantum memories. A single driven electron in a quantum dot can deterministically excite low-energy collective modes of a nuclear spin ensemble in the presence of lattice strain. We propose to gate a quantum state transfer between this central electron and these low-energy excitations—spin waves—in the presence of a strong magnetic field, where the nuclear coherence time is long. We develop a microscopic theory capable of calculating the exact time evolution of the strained electron-nuclear system. With this, we evaluate the operation of quantum state storage and show that fidelities up to 90% can be reached with a modest nuclear polarization of only 50%. These findings demonstrate that strain-enabled nuclear spin waves are a highly suitable candidate for quantum memory.We thank E. Chekhovich for helpful discussions. This work was supported by the ERC PHOENICS grant (617985), the EPSRC Quantum Technology Hub NQIT (EP/M013243/1), and the Royal Society (RGF/EA/181068). D. A. G. acknowledges support from St. John’s College Title A Fellowship. E. V. D. and J. M. acknowledge funding from the Danish Council for Independent Research (Grant No. DFF-4181-00416). C. L. G. acknowledges support from a Royal Society Dorothy Hodgkin Fellowship
Quantum light-matter interaction and controlled phonon scattering in a photonic Fano cavity
The Fano effect arises from the interference between a continuum of
propagating modes and a localised resonance. By using this resonance as one of
the mirrors in an optical cavity, a localised mode with a highly asymmetric
line shape is obtained. Placing a single quantum emitter inside the cavity
leads to a new regime of cavity quantum electrodynamics, where the light-matter
interaction dynamics is fundamentally different from that observed in a
conventional cavity with Lorenztian lineshape. Furthermore, when the
vibrational dynamics of the emitter is taken into account, an intricate
phonon-photon interplay arises, and the optical interference induced by the
Fano mirror significantly alters the leakage of energy into vibrational modes.
We demonstrate that this control mechanism improves the maximum attainable
indistinguishability of emitted photons, as compared to an equivalent cavity
with a conventional mirror
Cavity-induced exciton localization and polariton blockade in two-dimensional semiconductors coupled to an electromagnetic resonator
Recent experiments have demonstrated strong light-matter coupling between
electromagnetic nanoresonators and pristine sheets of two-dimensional
semiconductors, and it has been speculated whether these systems can enter the
quantum regime operating at the few-polariton level. To address this question,
we present a first-principles microscopic quantum theory for the interaction
between excitons in an infinite sheet of two-dimensional material and a
localised electromagnetic resonator. We find that the light-matter interaction
breaks the symmetry of the otherwise translation-invariant system and thereby
effectively generates a localised exciton mode, which is coupled to an
environment of residual exciton modes. This dissipative coupling increases with
tighter lateral confinement, and our analysis reveals this to be a potential
challenge in realising nonlinear exciton-exciton interaction. Nonetheless, we
predict that polariton blockade due to nonlinear exciton-exciton interactions
is well within reach for nanoresonators coupled to transition-metal
dichalcogenides, provided that the lateral resonator mode confinement can be
sufficiently small that the nonlinearity overcomes the polariton dephasing
caused by phonon interactions
Quantum theory of two-dimensional materials coupled to electromagnetic resonators
We present a microscopic quantum theory of light-matter interaction in
pristine sheets of two-dimensional semiconductors coupled to localized
electromagnetic resonators such as optical nanocavities or plasmonic particles.
The light-matter interaction breaks the translation symmetry of excitons in the
two-dimensional lattice, and we find that this symmetry-breaking interaction
leads to the formation of a localized exciton state, which mimics the spatial
distribution of the electromagnetic field of the resonator. The localized
exciton state is in turn coupled to an environment of residual exciton states.
We quantify the influence of the environment and find that it is most
pronounced for small lateral confinement length scales of the electromagnetic
field in the resonator, and that environmental effects can be neglected if this
length scale is sufficiently large. The microscopic theory provides a
physically appealing derivation of the coupled oscillator models widely used to
model experiments on these types of systems, in which all observable quantities
are directly derived from the material parameters and the properties of the
resonant electromagnetic field. As a consistency check, we show that the theory
recovers the results of semiclassical electromagnetic calculations and
experimental measurements of the excitonic dielectric response in the linear
excitation limit. The theory, however, is not limited to linear response, and
in general describes nonlinear exciton-exciton interactions in the localized
exciton state, thereby providing a powerful means of investigating the
nonlinear optical response of such systems
Dynamics and condensation of polaritons in an optical nanocavity coupled to two-dimensional materials
We present a comprehensive investigation of the light-matter interaction dynamics in two-dimensional materials coupled with a spectrally isolated cavity mode in the strong coupling regime. The interaction between light and matter breaks the translational symmetry of excitons in the two-dimensional lattice and results in the emergence of a localized polariton state. Employing an approach involving transformation to exciton reaction coordinates, we derive a Markovian master equation to describe the formation of a macroscopic population in the localized polariton state. Our study shows that the construction of a large-scale polariton population is affected by correction terms addressing the breakdown of translational symmetry. Increasing the spatial width of the cavity mode increases the Coulomb scattering rates while the correction terms saturate and affect the system's dynamics progressively less. Tuning the lattice temperature can induce bistability and hysteresis with different origins than those recognized for quantum wells in larger microcavities. We identify a limit temperature Tl as a key factor for stimulated emissions and forming a macroscopic population, enriching our understanding of strong coupling dynamics in systems with extreme confinement.</p
Cavity-waveguide interplay in optical resonators and its role in optimal single-photon sources
Interfacing solid-state emitters with photonic structures is a key strategy
for developing highly efficient photonic quantum technologies. Such structures
are often organised into two distinct categories: nanocavities and waveguides.
However, any realistic nanocavity structure simultaneously has characteristics
of both a cavity and waveguide, which is particularly pronounced when the
cavity is constructed using low-reflectivity mirrors in a waveguide structure
with good transverse light confinement. In this regime, standard cavity quantum
optics theory breaks down, as the waveguide character of the underlying
dielectric is only weakly suppressed by the cavity mirrors. By consistently
treating the photonic density of states of the structure, we provide a
microscopic description of an emitter including the effects of phonon
scattering over the full transition range from waveguide to cavity. This
generalised theory lets us identify an optimal regime of operation for
single-photon sources in optical nanostructures, where cavity and waveguide
effects are concurrently exploited