208 research outputs found
Double Quantum Dot Floquet Gain Medium
Strongly driving a two-level quantum system with light leads to a ladder of
Floquet states separated by the photon energy. Nanoscale quantum devices allow
the interplay of confined electrons, phonons, and photons to be studied under
strong driving conditions. Here we show that a single electron in a
periodically driven DQD functions as a "Floquet gain medium," where population
imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern
of gain and loss features in the cavity response. We further measure a large
intra-cavity photon number n_c in the absence of a cavity drive field, due to
equilibration in the Floquet picture. Our device operates in the absence of a
dc current -- one and the same electron is repeatedly driven to the excited
state to generate population inversion. These results pave the way to future
studies of non-classical light and thermalization of driven quantum systems
Threshold Dynamics of a Semiconductor Single Atom Maser
We demonstrate a single-atom maser consisting of a semiconductor double
quantum dot (DQD) that is embedded in a high quality factor microwave cavity. A
finite bias drives the DQD out of equilibrium, resulting in sequential single
electron tunneling and masing. We develop a dynamic tuning protocol that allows
us to controllably increase the time-averaged repumping rate of the DQD at a
fixed level detuning, and quantitatively study the transition through the
masing threshold. We further examine the crossover from incoherent to coherent
emission by measuring the photon statistics across the masing transition. The
observed threshold behavior is in agreement with an existing single atom maser
theory when small corrections from lead emission are taken into account
Spin Transport in a Mott Insulator of Ultracold Fermions
Strongly correlated materials are expected to feature unconventional
transport properties, such that charge, spin, and heat conduction are
potentially independent probes of the dynamics. In contrast to charge
transport, the measurement of spin transport in such materials is highly
challenging. We observed spin conduction and diffusion in a system of ultracold
fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong
interactions, spin diffusion is driven by super-exchange and
doublon-hole-assisted tunneling, and strongly violates the quantum limit of
charge diffusion. The technique developed in this work can be extended to
finite doping, which can shed light on the complex interplay between spin and
charge in the Hubbard model.Comment: 16 pages, 10 figure
Dynamic changes in host-virus interactions associated with colony founding and social environment in fire ant queens (Solenopsis invicta)
Funding Information US Department of Agriculture AFRI Award. Grant Number: 2009‐35302‐05301 Marie Curie International Incoming Fellowship. Grant Number: FP7‐PEOPLE‐2013‐IIF‐625487Peer reviewedPublisher PD
- …