1,642 research outputs found
Two-dimensional topological quantum walks in the momentum space of structured light
Quantum walks are powerful tools for quantum applications and for designing
topological systems. Although they are simulated in a variety of platforms,
genuine two-dimensional realizations are still challenging. Here we present an
innovative approach to the photonic simulation of a quantum walk in two
dimensions, where walker positions are encoded in the transverse wavevector
components of a single light beam. The desired dynamics is obtained by means of
a sequence of liquid-crystal devices, which apply polarization-dependent
transverse "kicks" to the photons in the beam. We engineer our quantum walk so
that it realizes a periodically-driven Chern insulator, and we probe its
topological features by detecting the anomalous displacement of the photonic
wavepacket under the effect of a constant force. Our compact, versatile
platform offers exciting prospects for the photonic simulation of
two-dimensional quantum dynamics and topological systems.Comment: Published version of the manuscrip
Observation of topological transport quantization by dissipation in fast Thouless pumps
Quantized dynamics is essential for natural processes and technological
applications alike. The work of Thouless on quantized particle transport in
slowly varying potentials (Thouless pumping) has played a key role in
understanding that such quantization may be caused not only by discrete
eigenvalues of a quantum system, but also by invariants associated with the
nontrivial topology of the Hamiltonian parameter space. Since its discovery,
quantized Thouless pumping has been believed to be restricted to the limit of
slow driving, a fundamental obstacle for experimental applications. Here, we
introduce non-Hermitian Floquet engineering as a new concept to overcome this
problem. We predict that a topological band structure and associated quantized
transport can be restored at driving frequencies as large as the system's band
gap. The underlying mechanism is suppression of non-adiabatic transitions by
tailored, time-periodic dissipation. We confirm the theoretical predictions by
experiments on topological transport quantization in plasmonic waveguide
arrays
Phase-control of directed diffusion in a symmetric optical lattice
We demonstrate the phenomenon of directed diffusion in a symmetric periodic
potential. This has been realized with cold atoms in a one-dimensional
dissipative optical lattice. The stochastic process of optical pumping leads to
a diffusive dynamics of the atoms through the periodic structure, while a
zero-mean force which breaks the temporal symmetry of the system is applied by
phase-modulating one of the lattice beams. The atoms are set into directed
motion as a result of the breaking of the temporal symmetry of the system
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