Ultrastrong coupling between a cavity resonator and the cyclotron transition of a 2D electron gas in the case of integer filling factor

We investigate theoretically the coupling between a cavity resonator and the cyclotron transition of a two dimensional electron gas under an applied perpendicular magnetic field. We derive and diagonalize an effective quantum Hamiltonian describing the magnetopolariton excitations of the two dimensional electron gas for the case of integer filling factors. The limits of validity of the present approach are critically discussed. The dimensionless vacuum Rabi frequency $\Omega_0/\omega_0$ (i.e., normalized to the cyclotron frequency $\omega_0$) is shown to scale as $\sqrt{\alpha\: n_{QW} \nu}$, where $\alpha$ is the fine structure constant, $n_{QW}$ is the number of quantum wells and $\nu$ is the filling factor in each well. We show that with realistic parameters of a high-mobility semiconductor two dimensional electron gas, the dimensionless coupling $\Omega_0/\omega_0$ can be much larger than 1 in the case of $\nu \gg 1$, the latter condition being typically realized for cyclotron transitions in the microwave range. Implications of such ultrastrong coupling regime are discussed

Cavity-assisted mesoscopic transport of fermions: Coherent and dissipative dynamics

We study the interplay between charge transport and light-matter interactions in a confined geometry, by considering an open, mesoscopic chain of two-orbital systems resonantly coupled to a single bosonic mode close to its vacuum state. We introduce and benchmark different methods based on self-consistent solutions of non-equilibrium Green's functions and numerical simulations of the quantum master equation, and derive both analytical and numerical results. It is shown that in the dissipative regime where the cavity photon decay rate is the largest parameter, the light-matter coupling is responsible for a steady-state current enhancement scaling with the cooperativity parameter. We further identify different regimes of interest depending on the ratio between the cavity decay rate and the electronic bandwidth. Considering the situation where the lower band has a vanishing bandwidth, we show that for a high-finesse cavity, the properties of the resonant Bloch state in the upper band are transfered to the lower one, giving rise to a delocalized state along the chain. Conversely, in the dissipative regime with low cavity quality factors, we find that the current enhancement is due to a collective decay of populations from the upper to the lower band.Comment: 52 pages, 11 figure

Ensemble-induced strong light-matter coupling of a single quantum emitter

We discuss a technique to strongly couple a single target quantum emitter to a cavity mode, which is enabled by virtual excitations of a nearby mesoscopic ensemble of emitters. A collective coupling of the latter to both the cavity and the target emitter induces strong photon non-linearities in addition to polariton formation, in contrast to common schemes for ensemble strong coupling. We demonstrate that strong coupling at the level of a single emitter can be engineered via coherent and dissipative dipolar interactions with the ensemble, and provide realistic parameters for a possible implementation with SiV$^{-}$ defects in diamond. Our scheme can find applications, amongst others, in quantum information processing or in the field of cavity-assisted quantum chemistry.Comment: 13 pages, 6 figures; substantially revised manuscript; see arXiv:1912.12703 for mathematical derivation

Anomalous diffusion in the Long-Range Haken-Strobl-Reineker model

We analyze the propagation of excitons in a $d$-dimensional lattice with power-law hopping $\propto 1/r^\alpha$ in the presence of dephasing, described by a generalized Haken-Strobl-Reineker model. We show that in the strong dephasing (quantum Zeno) regime the dynamics is described by a classical master equation for an exclusion process with long jumps. In this limit, we analytically compute the spatial distribution, whose shape changes at a critical value of the decay exponent $\alpha_{\rm cr} = (d+2)/2$. The exciton always diffuses anomalously: a superdiffusive motion is associated to a L\'evy stable distribution with long-range algebraic tails for $\alpha\leq\alpha_{\rm cr}$, while for $\alpha > \alpha_{\rm cr}$ the distribution corresponds to a surprising mixed Gaussian profile with long-range algebraic tails, leading to the coexistence of short-range diffusion and long-range L\'evy-flights. In the many-exciton case, we demonstrate that, starting from a domain-wall exciton profile, algebraic tails appear in the distributions for any $\alpha$, which affects thermalization: the longer the hopping range, the faster equilibrium is reached. Our results are directly relevant to experiments with cold trapped ions, Rydberg atoms and supramolecular dye aggregates. They provide a way to realize an exclusion process with long jumps experimentally.Comment: 5 pages, 2 figure

Non-Invasive Time-Lapsed Monitoring and Quantification of Engineered Bone-Like Tissue

The formation of bone-like tissue from human mesenchymal stem cells (hMSC) cultured in osteogenic medium on silk fibroin scaffolds was monitored and quantified over 44days in culture using non-invasive time-lapsed micro-computed tomography (μCT). Each construct was imaged nine times insitu. From μCT imaging, detailed morphometrical data on bone volume density, surface-to-volume ratio, trabecular thickness, trabecular spacing, and the structure model index and tissue mineral density were obtained. μCT irradiation did not impact the osteogenic performance of hMSCs based on DNA content, alkaline phosphatase activity, and calcium deposition when compared to non-exposed control samples. Bone-like tissue formation initiated at day 10 of the culture with the deposition of small mineralized clusters. Tissue mineral density increased linearly over time. The surface-to-volume ratio of the bone-like tissues converged asymptotically to 26mm−1. Although in vitro formation of bone-like tissue started from clusters, the overall bone volume was not predictable from the time, number, and size of initially formed bone-like clusters. Based on microstructural analysis, the morphometry of the tissue-engineered constructs was found to be in the range of human trabecular bone. In future studies, non-invasive, time-lapsed monitoring may enable researchers to culture tissues in vitro, right until the development of a desired morphology is accomplished. Our data demonstrate the feasibility of qualitatively and quantitatively detailing the spatial and temporal mineralization of bone-like tissue formation in tissue engineerin

Ultrastrong coupling of the cyclotron transition of a two-dimensional electron gas to a THz metamaterial

Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems, due to the possibility of manipulating the cavity quantum electrodynamic ground state with controllable physical properties. We report here experiments showing ultrastrong light-matter coupling in a terahertz metamaterial where the cyclotron transition of a high mobility two-dimensional electron gas is coupled to the photonic modes of an array of electronic split-ring resonators. We observe a normalized coupling ratio $\frac{\Omega}{\omega_c}=0.58$ between the vacuum Rabi frequency $\Omega$ and the cyclotron frequency $\omega_c$. Our system appears to be scalable in frequency and could be brought to the microwave spectral range with the potential of strongly controlling the magnetotransport properties of a high-mobility 2DEG

Ultrastrong photon-photon coupling

Correlations between photons are a key feature of nonclassical states of light. Recent studies suggest that the ground state of a cavity quantum electrodynamics system can have light-matter correlations in the form of a squeezed vacuum state in thermal equilibrium when the matter ultrastrongly couples with cavity photons. This raises a question whether different photonic modes can also be correlated in the ground state via ultrastrong light-matter coupling. Here we demonstrate ultrastrong coupling between photonic modes of a multi-mode three-dimensional terahertz photonic-crystal cavity that is mediated by their simultaneous ultrastrong coupling with the cyclotron resonance of a two-dimensional electron gas in GaAs. Terahertz spectroscopy measurements of Landau polaritons showed excellent agreement with our calculations based on a microscopic quantum model. Despite the lack of nonlinearity in the matter system, the model shows significant correlations between the photonic modes in the ground state of the system, which can be controlled by changing the matter and photon frequencies and the spatial overlap of their mode profiles. We propose a detuning-independent figure of merit to quantify all possible couplings in multi-mode systems. These findings pave the way for creating multi-mode nonclassical states and exploring the many-body regime of quantum optics with vacuum fields.Comment: 32 pages, 12 figure