34 research outputs found
Perpetual emulation threshold of PT-symmetric Hamiltonians
We describe a technique to emulate a two-level \PT-symmetric spin
Hamiltonian, replete with gain and loss, using only the unitary dynamics of a
larger quantum system. This we achieve by embedding the two-level system in
question in a subspace of a four-level Hamiltonian. Using an \textit{amplitude
recycling} scheme that couples the levels exterior to the \PT-symmetric
subspace, we show that it is possible to emulate the desired behaviour of the
\PT-symmetric Hamiltonian without depleting the exterior, reservoir levels. We
are thus able to extend the emulation time indefinitely, despite the
non-unitary \PT dynamics. We propose a realistic experimental implementation
using dynamically decoupled magnetic sublevels of ultracold atoms.Comment: 15 pages, 8 figure
Synthetic clock transitions via continuous dynamical decoupling
Decoherence of quantum systems due to uncontrolled fluctuations of the
environment presents fundamental obstacles in quantum science. `Clock'
transitions which are insensitive to such fluctuations are used to improve
coherence, however, they are not present in all systems or for arbitrary system
parameters. Here, we create a trio of synthetic clock transitions using
continuous dynamical decoupling in a spin-1 Bose-Einstein condensate in which
we observe a reduction of sensitivity to magnetic field noise of up to four
orders of magnitude; this work complements the parallel work by Anderson et al.
(submitted, 2017). In addition, using a concatenated scheme, we demonstrate
suppression of sensitivity to fluctuations in our control fields. These
field-insensitive states represent an ideal foundation for the next generation
of cold atom experiments focused on fragile many-body phases relevant to
quantum magnetism, artificial gauge fields, and topological matter.Comment: 8 pages, 4 figures, Supplemental material
Fourier transform spectroscopy of a spin-orbit coupled Bose gas
We describe a Fourier transform spectroscopy technique for directly measuring
band structures, and apply it to a spin-1 spin-orbit coupled Bose-Einstein
condensate. In our technique, we suddenly change the Hamiltonian of the system
by adding a spin-orbit coupling interaction and measure populations in
different spin states during the subsequent unitary evolution. We then
reconstruct the spin and momentum resolved spectrum from the peak frequencies
of the Fourier transformed populations. In addition, by periodically modulating
the Hamiltonian, we tune the spin-orbit coupling strength and use our
spectroscopy technique to probe the resulting dispersion relation. The
frequency resolution of our method is limited only by the coherent evolution
timescale of the Hamiltonian and can otherwise be applied to any system, for
example, to measure the band structure of atoms in optical lattice potentials
(py)LIon: a package for simulating trapped ion trajectories
The (py)LIon package is a set of tools to simulate the classical trajectories
of ensembles of ions in electrodynamic traps. Molecular dynamics simulations
are performed using LAMMPS, an efficient and feature-rich program. (py)LIon has
been validated by comparison with the analytic theory describing ion trap
dynamics. Notable features include GPU-accelerated force calculations, and
treating collections of ions as rigid bodies to enable investigations of the
rotational dynamics of large, mesoscopic charged particles.Comment: 11 pages, 9 figure
Sub-Doppler laser cooling of potassium atoms
We investigate sub-Doppler laser cooling of bosonic potassium isotopes, whose
small hyperfine splitting has so far prevented cooling below the Doppler
temperature. We find instead that the combination of a dark optical molasses
scheme that naturally arises in this kind of systems and an adiabatic ramping
of the laser parameters allows to reach sub-Doppler temperatures for small
laser detunings. We demonstrate temperatures as low as 25(3)microK and
47(5)microK in high-density samples of the two isotopes 39K and 41K,
respectively. Our findings will find application to other atomic systems.Comment: 7 pages, 9 figure
Repeated Measurements with Minimally Destructive Partial-Transfer Absorption Imaging
We demonstrate partial-transfer absorption imaging as a technique for repeatedly imaging an ultracold atomic ensemble with minimal perturbation. We prepare an atomic cloud in a state that is dark to the imaging light. We then use a microwave pulse to coherently transfer a small fraction of the ensemble to a bright state, which we image using in situ absorption imaging. The amplitude or duration of the microwave pulse controls the fractional transfer from the dark to the bright state. For small transfer fractions, we can image the atomic cloud up to 50 times before it is depleted. As a sample application, we repeatedly image an atomic cloud oscillating in a dipole trap to measure the trap frequency
Unconventional topology with a Rashba spin-orbit coupled quantum gas
Topological order can be found in a wide range of physical systems, from
crystalline solids, photonic meta-materials and even atmospheric waves to
optomechanic, acoustic and atomic systems. Topological systems are a robust
foundation for creating quantized channels for transporting electrical current,
light, and atmospheric disturbances. These topological effects are quantified
in terms of integer-valued invariants, such as the Chern number, applicable to
the quantum Hall effect, or the invariant suitable for
topological insulators. Here we engineered Rashba spin-orbit coupling for a
cold atomic gas giving non-trivial topology, without the underlying crystalline
structure that conventionally yields integer Chern numbers. We validated our
procedure by spectroscopically measuring the full dispersion relation, that
contained only a single Dirac point. We measured the quantum geometry
underlying the dispersion relation and obtained the topological index using
matter-wave interferometry. In contrast to crystalline materials, where
topological indices take on integer values, our continuum system reveals an
unconventional half-integer Chern number, potentially implying new forms of
topological transport