19 research outputs found
Quantum dynamics of an atomic double-well system interacting with a trapped ion
We theoretically analyze the dynamics of an atomic double-well system with a
single ion trapped in its center. We find that the atomic tunnelling rate
between the wells depends both on the spin of the ion via the short-range
spin-dependent atom-ion scattering length and on its motional state with
tunnelling rates reaching hundreds of Hz. A protocol is presented that could
transport an atom from one well to the other depending on the motional (Fock)
state of the ion within a few ms. This phonon-atom coupling is of interest for
creating atom-ion entangled states and may form a building block in
constructing a hybrid atom-ion quantum simulator. We also analyze the effect of
imperfect ground state cooling of the ion and the role of micromotion when the
ion is trapped in a Paul trap. Due to the strong non-linearities in the
atom-ion interaction, the micromotion can cause couplings to high energy
atom-ion scattering states, preventing accurate state preparation and
complicating the double-well dynamics. We conclude that the effects of
micromotion can be reduced by choosing ion/atom combinations with a large mass
ratio and by choosing large inter-well distances. The proposed double-well
system may be realised in an experiment by combining either optical traps or
magnetic microtraps for atoms with ion trapping technology.Comment: 14 pages, 13 figure
Signal processing techniques for efficient compilation of controlled rotations in trapped ions
Quantum logic gates with many control qubits are essential in many quantum
algorithms, but remain challenging to perform in current experiments. Trapped
ion quantum computers natively feature a different type of entangling
operation, namely the Molmer-Sorensen (MS) gate which effectively applies an
Ising interaction to all qubits at the same time. We consider a sequence of
equal all-to-all MS operations, interleaved with single qubit gates that act
only on one special qubit. Using a connection with quantum signal processing
techniques, we find that it is possible to perform an arbitray SU(2) rotation
on the special qubit if and only if all other qubits are in the state |1>. Such
controlled rotation gates with N-1 control qubits require 2N applications of
the MS gate, and can be mapped to a conventional Toffoli gate by demoting a
single qubit to ancilla.Comment: 14 pages, 3 figures, comments welcome. v3 includes several fixes and
adds an appendix with explicit angle
Controlled long-range interactions between Rydberg atoms and ions
We theoretically investigate trapped ions interacting with atoms that are
coupled to Rydberg states. The strong polarizabilities of the Rydberg levels
increases the interaction strength between atoms and ions by many orders of
magnitude, as compared to the case of ground state atoms, and may be mediated
over micrometers. We calculate that such interactions can be used to generate
entanglement between an atom and the motion or internal state of an ion.
Furthermore, the ion could be used as a bus for mediating spin-spin
interactions between atomic spins in analogy to much employed techniques in ion
trap quantum simulation. The proposed scheme comes with attractive features as
it maps the benefits of the trapped ion quantum system onto the atomic one
without obviously impeding its intrinsic scalability. No ground state cooling
of the ion or atom is required and the setup allows for full dynamical control.
Moreover, the scheme is to a large extent immune to the micromotion of the ion.
Our findings are of interest for developing hybrid quantum information
platforms and for implementing quantum simulations of solid state physics.Comment: 20 pages including appendices, 6 figure
Spectroscopy of the ^2S_{1/2} \rightarrow\,^2P_{3/2} transition in Yb II: Isotope shifts, hyperfine splitting and branching ratios
We report on spectroscopic results on the ^2S_{1/2} \rightarrow\,^2P_{3/2}
transition in single trapped Yb ions. We measure the isotope shifts for all
stable Yb isotopes except Yb, as well as the hyperfine
splitting of the state in Yb. Our results are in
agreement with previous measurements but are a factor of 5-9 more precise. For
the hyperfine constant MHz our results
also agree with previous measurements but deviate significantly from
theoretical predictions. We present experimental results on the branching
ratios for the decay of the state. We find branching fractions for
the decay to the state and state of 0.17(1)% and
1.08(5)%, respectively, in rough agreement with theoretical predictions.
Furthermore, we measured the isotope shifts of the ^2F_{7/2}
\rightarrow\,^1D\left[5/2\right]_{5/2} transition and determine the hyperfine
structure constant for the state in Yb
to be MHz.Comment: 6 pages, 4 figure
Operation of a Microfabricated Planar Ion-Trap for Studies of a Yb-Rb Hybrid Quantum System
In order to study interactions of atomic ions with ultracold neutral atoms,
it is important to have sub-m control over positioning ion crystals.
Serving for this purpose, we introduce a microfabricated planar ion trap
featuring 21 DC electrodes. The ion trap is controlled by a home-made FPGA
voltage source providing independently variable voltages to each of the DC
electrodes. To assure stable positioning of ion crystals with respect to
trapped neutral atoms, we integrate into the overall design a compact mirror
magneto optical chip trap (mMOT) for cooling and confining neutral Rb
atoms. The trapped atoms will be transferred into an also integrated chipbased
Ioffe-Pritchard trap potential formed by a Z-shaped wire and an external bias
magnetic field.We introduce the hybrid atom-ion chip, the microfabricated
planar ion trap and use trapped ion crystals to determine ion lifetimes, trap
frequencies, positioning ions and the accuracy of the compensation of
micromotion.Comment: 10 pages, 13 figure
Dynamics of a single ion spin impurity in a spin-polarized atomic bath
We report on observations of spin dynamics in single Yb ions immersed in
a cold cloud of spin-polarized Li atoms. This species combination has been
proposed to be the most suitable system to reach the quantum regime in atom-ion
experiments. For Yb, we find that the atomic bath polarizes the
spin of the ion by 93(4)\,\% after a few Langevin collisions, pointing to
strong spin-exchange rates. For the hyperfine ground states of Yb,
we also find strong rates towards spin polarization. However, relaxation
towards the ground state occurs after 7.7(1.5) Langevin collisions. We
investigate spin impurity atoms as possible source of apparent spin-relaxation
leading us to interpret the observed spin-relaxation rates as an upper limit.
Using ab initio electronic structure and quantum scattering calculations, we
explain the observed rates and analyze their implications for the possible
observation of Feshbach resonances between atoms and ions once the quantum
regime is reached.Comment: 10 pages, 11 figure
Dynamics of a trapped ion in a quantum gas:Effects of particle statistics
We study the quantum dynamics of an ion confined in a radiofrequency trap in
interaction with either a Bose or spin-polarized Fermi gas. To this end, we
derive quantum optical master equations in the limit of weak coupling and the
Lamb-Dicke approximations. For the bosonic bath, we also include the so-called
"Lamb-shift" correction to the ion trap due to the coupling to the quantum gas
as well as the extended Fr\"ohlich interaction within the Bogolyubov
approximation that have been not considered in previous studies. We calculate
the ion kinetic energy for various atom-ion scattering lengths as well as gas
temperatures by considering the intrinsic micromotion and we analyse the
damping of the ion motion in the gas as a function of the gas temperature. We
find that the ion's dynamics depends on the quantum statistics of the gas and
that a fermionic bath enables to attain lower ionic energies.Comment: 25 pages, 9 figure
Controlling the nature of a charged impurity in a bath of Feshbach dimers
We theoretically study the dynamics of a trapped ion that is immersed in an
ultracold gas of weakly bound atomic dimers created by a Feshbach resonance.
Using quasi-classical simulations, we find a crossover from dimer dissociation
to molecular ion formation depending on the binding energy of the dimers. The
location of the crossover strongly depends on the collision energy and the
time-dependent fields of the Paul trap. Deeply bound dimers lead to fast
molecular ion formation, with rates approaching the Langevin collision rate
cms. The kinetic energies
of the created molecular ions have a median below mK, such that they will
stay confined in the ion trap. We conclude that interacting ions and Feshbach
molecules may provide a novel approach towards the creation of ultracold
molecular ions with applications in precision spectroscopy and quantum
chemistry.Comment: 9 pages and 12 figures including appendice
Signal processing techniques for efficient compilation of controlled rotations in trapped ions
Quantum logic gates with many control qubits are essential in many quantum algorithms, but remain challenging to perform in current experiments. Trapped ion quantum computers natively feature the M\xc3\xb8lmer-S\xc3\xb8rensen (MS) entangling operation, which effectively applies an Ising interaction to all pairs of qubits at the same time. We consider a sequence of equal all-to-all MS operations, interleaved with single-qubit gates that act only on one special qubit. Using a connection with quantum signal processing techniques, we find that it is possible to perform an arbitray SU(2) rotation on the special qubit if and only if all other qubits are in the state \xe2\x89\xa4. Such controlled rotation gates with N - 1 control qubits require 2N applications of the MS gate, and can be mapped to a conventional Toffoli gate by demoting a single qubit to ancilla