Dissipative Bose-Einstein condensation in contact with a thermal reservoir

We investigate the real-time dynamics of open quantum spin-$1/2$ or hardcore boson systems on a spatial lattice, which are governed by a Markovian quantum master equation. We derive general conditions under which the hierarchy of correlation functions closes such that their time evolution can be computed semi-analytically. Expanding our previous work [Phys. Rev. A 93, 021602 (2016)] we demonstrate the universality of a purely dissipative quantum Markov process that drives the system of spin-$1/2$ particles into a totally symmetric superposition state, corresponding to a Bose-Einstein condensate of hardcore bosons. In particular, we show that the finite-size scaling behavior of the dissipative gap is independent of the chosen boundary conditions and the underlying lattice structure. In addition, we consider the effect of a uniform magnetic field as well as a coupling to a thermal bath to investigate the susceptibility of the engineered dissipative process to unitary and nonunitary perturbations. We establish the nonequilibrium steady-state phase diagram as a function of temperature and dissipative coupling strength. For a small number of particles $N$, we identify a parameter region in which the engineered symmetrizing dissipative process performs robustly, while in the thermodynamic limit $N\rightarrow \infty$, the coupling to the thermal bath destroys any long-range order.Comment: 30 pages, 8 figures; Revised version: Minor changes and references adde

Preparation for Quantum Simulation of the 1+1D O(3) Non-linear {\sigma}-Model using Cold Atoms

The 1+1D O(3) non-linear {\sigma}-model is a model system for future quantum lattice simulations of other asymptotically-free theories, such as non-Abelian gauge theories. We find that utilizing dimensional reduction can make efficient use of two-dimensional layouts presently available on cold atom quantum simulators. A new definition of the renormalized coupling is introduced, which is applicable to systems with open boundary conditions and can be measured using analog quantum simulators. Monte Carlo and tensor network calculations are performed to determine the quantum resources required to reproduce perturbative short-distance observables. In particular, we show that a rectangular array of 48 Rydberg atoms with existing quantum hardware capabilities should be able to adiabatically prepare low-energy states of the perturbatively-matched theory. These states can then be used to simulate non-perturbative observables in the continuum limit that lie beyond the reach of classical computers.Comment: 12 pages, 5 figures, 2 tables, published versio

State Preparation in the Heisenberg Model through Adiabatic Spiraling

An adiabatic state preparation technique, called the adiabatic spiral, is proposed for the Heisenberg model. This technique is suitable for implementation on a number of quantum simulation platforms such as Rydberg atoms, trapped ions, or superconducting qubits. Classical simulations of small systems suggest that it can be successfully implemented in the near future. A comparison to Trotterized time evolution is performed and it is shown that the adiabatic spiral is able to outperform Trotterized adiabatics.Comment: 22 pages, 8 figures, published versio

Simulating Heisenberg Interactions in the Ising Model with Strong Drive Fields

The time-evolution of an Ising model with large driving fields over discrete time intervals is shown to be reproduced by an effective XXZ-Heisenberg model at leading order in the inverse field strength. For specific orientations of the drive field, the dynamics of the XXX-Heisenberg model is reproduced. These approximate equivalences, valid above a critical driving field strength set by dynamical phase transitions in the Ising model, are expected to enable quantum devices that natively evolve qubits according to the Ising model to simulate more complex systems.Comment: 10 pages, 5 figures, accepted versio

Meron- and Semi-Vortex-Clusters as Physical Carriers of Topological Charge and Vorticity

In O($N$) non-linear $\sigma$-models on the lattice, the Wolff cluster algorithm is based on rewriting the functional integral in terms of mutually independent clusters. Through improved estimators, the clusters are directly related to physical observables. In the $(N-1)$-d O($N$) model (with an appropriately constrained action) the clusters carry an integer or half-integer topological charge. Clusters with topological charge $\pm 1/2$ are denoted as merons. Similarly, in the 2-d O(2) model the clusters carry pairs of semi-vortices and semi-anti-vortices (with vorticity $\pm 1/2$) at their boundary. Using improved estimators, meron- and semi-vortex-clusters provide analytic insight into the topological features of the dynamics. We show that the histograms of the cluster-size distributions scale in the continuum limit, with a fractal dimension $D$, which suggests that the clusters are physical objects. We demonstrate this property analytically for merons and non-merons in the 1-d O(2) model (where $D=1$), and numerically for the 2-d O(2), 2-d O(3), and 3-d O(4) model, for which we observe fractal dimensions $D < d$. In the vicinity of a critical point, a scaling law relates $D$ to a combination of critical exponents. In the 2-d O(3) model, meron- and multi-meron-clusters are responsible for a logarithmic ultraviolet divergence of the topological susceptibility.Comment: 14 pages, 5 figures, presented at the 37th International Symposium on Lattice Field Theory - Lattice 2019, 16-22 June 2019, Wuhan, Chin

Efficient stray-light suppression for resonance fluorescence in quantum dot-micropillars using self-aligned metal apertures

Within this work we propose and demonstrate a technological approach to efficiently suppress excitation laser stray-light in resonance fluorescence experiments on quantum dot-micropillars. To ensure efficient stray-light suppression, their fabrication process includes a planarization step and the subsequent covering with a titanium mask to fabricate self-aligned apertures at the micropillar positions. These apertures aim at limiting laser straylight in side-excitation vertical-detection configuration, while enabling detection of the optical signal through the top facet of the micropillars. Beneficial effects of these apertures are proven and quantitatively evaluated within a statistical study in which we determine and compare the stray-light suppression of 48 micropillars with and without metal apertures. Actual resonance fluorescence experiments on single quantum dots coupled to the cavity mode prove the relevance of the proposed approach and demonstrate that it will foster further studies on cavity quantum electrodynamics phenomena under coherent optical excitation.PostprintPeer reviewe

Transition from Jaynes-Cummings to Autler-Townes ladder in a quantum dot-microcavity system

The research leading to these results has received funding from the German Research Foundation (DFG) via Projects No. Ka2318/4-1 and No. Re2974/3-1, the SFB 787 "Semiconductor Nanophotonics: Materials, Models, Devices", and from the European Research Council under the European Union's Seventh Framework ERC Grant Agreement No. 615613. A. C. gratefully acknowledges support from SFB 910: "Control of self-organizing nonlinear systems".We study experimentally and theoretically a coherently-driven strongly-coupled quantum dot-microcavity system. Our focus is on physics of the unexplored intermediate excitation regime where the resonant laser field dresses a strongly-coupled single exciton-photon (polariton) system resulting in a ladder of laser-dressed Jaynes-Cummings states. In that case both the coupling of the emitter to the confined light field of the microcavity and to the light field of the external laser are equally important, as proved by observation of injection pulling of the polariton branches by an external laser. This intermediate interaction regime is of particular interest since it connects the purely quantum mechanical Jaynes-Cummings ladder and the semi-classical Autler-Townes ladder. Exploring the driving strength-dependence of the mutually coupled system we establish the maximum in the resonance fluorescence signal to be a robust fingerprint of the intermediate regime and observe signatures indicating the laser-dressed Jaynes-Cummings ladder. In order to address the underlying physics we excite the coupled system via the matter component of fermionic nature undergoing saturation - in contrast to commonly used cavity-mediated excitation.PostprintPeer reviewe

Doubled lattice Chern–Simons–Yang–Mills theories with discrete gauge group

We construct doubled lattice Chern–Simons–Yang–Mills theories with discrete gauge group G in the Hamiltonian formulation. Here, these theories are considered on a square spatial lattice and the fundamental degrees of freedom are defined on pairs of links from the direct lattice and its dual, respectively. This provides a natural lattice construction for topologically-massive gauge theories, which are invariant under parity and time-reversal symmetry. After defining the building blocks of the doubled theories, paying special attention to the realization of gauge transformations on quantum states, we examine the dynamics in the group space of a single cross, which is spanned by a single link and its dual. The dynamics is governed by the single-cross electric Hamiltonian and admits a simple quantum mechanical analogy to the problem of a charged particle moving on a discrete space affected by an abstract electromagnetic potential. Such a particle might accumulate a phase shift equivalent to an Aharonov–Bohm phase, which is manifested in the doubled theory in terms of a nontrivial ground-state degeneracy on a single cross. We discuss several examples of these doubled theories with different gauge groups including the cyclic group Z(k)⊂U(1), the symmetric group S3⊂O(2), the binary dihedral (or quaternion) group View the MathML source, and the finite group Δ(27)⊂SU(3). In each case the spectrum of the single-cross electric Hamiltonian is determined exactly. We examine the nature of the low-lying excited states in the full Hilbert space, and emphasize the role of the center symmetry for the confinement of charges. Whether the investigated doubled models admit a non-Abelian topological state which allows for fault-tolerant quantum computation will be addressed in a future publication

Environmental signals rather than layered ontogeny imprint the function of type 2 conventional dendritic cells in young and adult mice

Conventional dendritic cells (cDC) are key activators of naive T cells, and can be targeted in adults to induce adaptive immunity, but in early life are considered under-developed or functionally immature. Here we show that, in early life, when the immune system develops, cDC2 exhibit a dual hematopoietic origin and, like other myeloid and lymphoid cells, develop in waves. Developmentally distinct cDC2 in early life, despite being distinguishable by fate mapping, are transcriptionally and functionally similar. cDC2 in early and adult life, however, are exposed to distinct cytokine environments that shape their transcriptional profile and alter their ability to sense pathogens, secrete cytokines and polarize T cells. We further show that cDC2 in early life, despite being distinct from cDC2 in adult life, are functionally competent and can induce T cell responses. Our results thus highlight the potential of harnessing cDC2 for boosting immunity in early life.</p