13 research outputs found
A subradiant optical mirror formed by a single structured atomic layer
Efficient and versatile interfaces for the interaction of light with matter
are an essential cornerstone for quantum science. A fundamentally new avenue of
controlling light-matter interactions has been recently proposed based on the
rich interplay of photon-mediated dipole-dipole interactions in structured
subwavelength arrays of quantum emitters. Here we report on the direct
observation of the cooperative subradiant response of a two-dimensional (2d)
square array of atoms in an optical lattice. We observe a spectral narrowing of
the collective atomic response well below the quantum-limited decay of
individual atoms into free space. Through spatially resolved spectroscopic
measurements, we show that the array acts as an efficient mirror formed by only
a single monolayer of a few hundred atoms. By tuning the atom density in the
array and by changing the ordering of the particles, we are able to control the
cooperative response of the array and elucidate the interplay of spatial order
and dipolar interactions for the collective properties of the ensemble. Bloch
oscillations of the atoms out of the array enable us to dynamically control the
reflectivity of the atomic mirror. Our work demonstrates efficient optical
metamaterial engineering based on structured ensembles of atoms and paves the
way towards the controlled many-body physics with light and novel light-matter
interfaces at the single quantum level.Comment: 8 pages, 5 figures + 12 pages Supplementary Infomatio
Floquet Prethermalization in a Bose-Hubbard System
Periodic driving has emerged as a powerful tool in the quest to engineer new
and exotic quantum phases. While driven many-body systems are generically
expected to absorb energy indefinitely and reach an infinite-temperature state,
the rate of heating can be exponentially suppressed when the drive frequency is
large compared to the local energy scales of the system -- leading to
long-lived 'prethermal' regimes. In this work, we experimentally study a
bosonic cloud of ultracold atoms in a driven optical lattice and identify such
a prethermal regime in the Bose-Hubbard model. By measuring the energy
absorption of the cloud as the driving frequency is increased, we observe an
exponential-in-frequency reduction of the heating rate persisting over more
than 2 orders of magnitude. The tunability of the lattice potentials allows us
to explore one- and two-dimensional systems in a range of different interacting
regimes. Alongside the exponential decrease, the dependence of the heating rate
on the frequency displays features characteristic of the phase diagram of the
Bose-Hubbard model, whose understanding is additionally supported by numerical
simulations in one dimension. Our results show experimental evidence of the
phenomenon of Floquet prethermalization, and provide insight into the
characterization of heating for driven bosonic systems
Realizing distance-selective interactions in a Rydberg-dressed atom array
Measurement-based quantum computing relies on the rapid creation of
large-scale entanglement in a register of stable qubits. Atomic arrays are well
suited to store quantum information, and entanglement can be created using
highly-excited Rydberg states. Typically, isolating pairs during gate operation
is difficult because Rydberg interactions feature long tails at large
distances. Here, we engineer distance-selective interactions that are strongly
peaked in distance through off-resonant laser coupling of molecular potentials
between Rydberg atom pairs. Employing quantum gas microscopy, we verify the
dressed interactions by observing correlated phase evolution using many-body
Ramsey interferometry. We identify atom loss and coupling to continuum modes as
a limitation of our present scheme and outline paths to mitigate these effects,
paving the way towards the creation of large-scale entanglement.Comment: 5 pages, 4 figures + supplementary informatio
Many-Body Delocalization in the Presence of a Quantum Bath
Closed generic quantum many-body systems may fail to thermalize under certain
conditions even after long times, a phenomenon called many-body localization
(MBL). Numerous studies support the stability of the MBL phase in strongly
disordered one-dimensional systems. However, the situation is much less clear
when a small part of the system is ergodic, a scenario which also has important
implications for the existence of many-body localization in higher dimensions.
Here we address this question experimentally using a large-scale quantum
simulator of ultracold bosons in a two-dimensional optical lattice. We prepare
two-component mixtures of varying relative population and implement a disorder
potential which is only experienced by one of the components. The second
non-disordered ''clean'' component plays the role of a bath of adjustable size
that is collisionally coupled to the ''dirty'' component. Our experiments show
how the dynamics of the dirty component, which, when on its own, show strong
evidence of localization, become affected by the coupling to the clean
component. For a high clean population, the clean component appears to behave
as an effective bath for the system which leads to its delocalization, while
for a smaller clean population, the ability of the bath to destabilize the
system becomes strongly reduced. Our results reveal how a finite-sized quantum
system can bring another one towards thermalization, in a regime of complex
interplay between disorder, tunneling and intercomponent interactions. They
provide a new benchmark for effective theories aiming to capture the complex
physics of MBL in the weakly localized regime