15 research outputs found
Leakage suppression by ultrafast pulse shaping
We consider the leakage suppression problem of a three-level system in which
the first two levels are the qubit system and the third, weakly-coupled to the
second, is the leakage state. We show that phase- and amplitude-controlled two
(three) pulses are sufficient for arbitrary qubit controls from the ground (an
arbitrary) initial state, with leakage suppressed up to the first order of
perturbation without additional pulse-area cost. A proof-of-principle
experiment was performed with shaped femtosecond optical pulses and atomic
rubidium showing a good agreement with the theory.Comment: 6 pages, 4 figure
Single-laser-pulse implementation of arbitrary ZYZ rotations of an atomic qubit
Arbitrary rotation of a qubit can be performed with a three-pulse sequence;
for example, ZYZ rotations. However, this requires precise control of the
relative phase and timing between the pulses, making it technically challenging
in optical implementation in a short time scale. Here we show any ZYZ rotations
can be implemented with a single laser-pulse, that is {\it a chirped pulse with
a temporal hole}. The hole of this shaped pulse induces a non-adiabatic
interaction in the middle of the adiabatic evolution of the chirped pulse,
converting the central part of an otherwise simple Z-rotation to a Y rotation,
constructing ZYZ rotations. The result of our experiment performed with shaped
femtosecond laser pulses and cold rubidium atoms shows strong agreement with
the theory.Comment: 5 pages 4 figure
Rabi oscillations of Morris-Shore transformed -state systems by elliptically polarized ultrafast laser pulses
We present an experimental investigation of ultrafast-laser driven Rabi
oscillations of atomic rubidium. Since the broadband spectrum of an ultrafast
laser pulse simultaneously couples all the electronic hyperfine transitions
between the excited and ground states, the complex excitation linkages involved
with the D1 or D2 transition are energy degenerate. Here, by applying the
Morris-Shore transformation, it is shown that this multi-state system is
reduced to a set of independent two-state systems and dark states. In
experiments performed by ultrafast laser interactions of atomic rubidium in the
strong interaction regime, we demonstrate that the ultrafast dynamics of the
considered multi-state system is governed by a sum of at most two decoupled
Rabi oscillations when this system interacts with ultrafast laser pulses of any
polarization state. We further show the implication of this result to possible
controls of photo-electron polarizations.Comment: 7 pages, 4 figure
Coherent and dissipative dynamics of entangled few-body systems of Rydberg atoms
Experimentally observed quantum few-body dynamics of neutral atoms excited to
a Rydberg state are numerically analyzed with Lindblad master equation
formalism. For this, up to five rubidium atoms are trapped with optical
tweezers, arranged in various two-dimensional configurations, and excited to
Rydberg 67S state in the nearest-neighbor blockade regime. Their coherent
evolutions are measured with time-varying ground-state projections. The
experimental results are analyzed with a model Lindblad equation with the
homogeneous and inhomogeneous dampings determined by systematic and statistical
error analysis. The coherent evolutions of the entangled systems are
successfully reproduced by the resulting model analysis for the experimental
results with optimal parameters in consistent with external calibrations.Comment: 7 pages, 4 figures, 1 tabl
Subpicosecond rotations of atomic clock states
We demonstrate subpicosecond-time-scale population transfer between the pair
of hyperfine ground states of atomic rubidium using a single laser-pulse. Our
scheme utilizes the geometric and dynamic phases induced during Rabi
oscillation through the fine-structure excited state in order to construct an
rotation gate for the hyperfine-state qubit system. Experiment performed
with a femtosecond laser and cold rubidium atoms, in a magneto-optical trap,
shows over 98\% maximal population transfer between the clock states.Comment: 5 pages, 5 figure
Ultrafast time-scale Berry-phase gates of atomic clock states
Extremely fast qubit controls can greatly reduce the calculation time in
quantum computation, and potentially resolve the finite-time decoherence issues
in many physical systems. Here, we propose and experimentally demonstrate
pico-second time-scale controls of atomic clock state qubits, using Berry-phase
gates implemented with a pair of chirped laser pulses. While conventional
methods of microwave or Raman transitions do not allow atomic qubit controls
within a time faster than the hyperfine free evolution period, our approach of
ultrafast Berry-phase gates accomplishes fast clock-state operations. We also
achieves operational robustness against laser parametric noises, since
geometric phases are determined by adiabatic evolution pathway only, without
being affected by any dynamic details. The experimental implementation is
conducted with two linearly polarized, chirped ultrafast optical pulses,
interacting with five single rubidium atoms in an array of optical tweezer
dipole traps, to demonstrate the proposed ultrafast clock-state gates and their
operational robustness.Comment: 9 pages, 5 figure
In situ single-atom array synthesis by dynamic holographic optical tweezers
Cooling and trapping of atoms by light has enabled one to build and
manipulate quantum systems at the single atom level. Such a bottom-up approach
becomes one of the fascinating challenges toward scalable and highly
controllable quantum systems, e.g., a large-scale quantum information machine.
Their implementation requires crucial pre-requisites: scalablity, site
distinguishability, and reliable single-atom loading into sites. The widely
adopted methods satisfies the two former conditions relatively well, but the
last condition, filling single atoms onto individual sites, relies mostly on
the probabilistic loading, implying that loading a pre-defined set of atoms in
given positions will be hampered exponentially. Two approaches are readily
thinkable to overcome this issue: increasing the single-atom loading efficiency
and relocating abundant atoms into unfilled positions. Realizing the relocation
is directly related to how many atoms can be transportable in a designer way.
Here, we demonstrate a dynamic holographic single-atom tweezers with
unprecedented degrees of freedom of 2N. In a proof-of-principle experiment
conducted with cold rubidium atoms, simultaneous rearrangements of N=9 single
atoms are successfully performed. This method may be further applicable to
deterministic N single-atom loading, coherent transport, and controlled
collisions.Comment: 6 pages. 4 figure
Rydberg atom entanglements in the weak coupling regime
We present an entanglement scheme for Rydberg atoms using the van der Waals
interaction phase induced by Ramsey-type pulsed interactions. This scheme
realizes not only controlled phase operations between atoms at a distance
larger than Rydberg blockade distance, but also various counter-intuitive
entanglement examples, including two-atom entanglement in the presence of a
closer third atom and -state generation for partially-blockaded three atoms.
Experimental realization is conducted with single rubidium atoms loaded in an
array of optical tweezer dipole traps, to demonstrate the proposed entanglement
generations and measurements.Comment: 5 pages, 4 figure
Quantum-Ising Hamiltonian programming in trio, quartet, and sextet qubit systems
Rydberg-atom quantum simulators are of keen interest because of their
possibilities towards high-dimensional qubit architectures. Here we report
three-dimensional conformation spectra of quantum-Ising Hamiltonian systems
with programmed qubit connections. With a Rydberg-atom quantum simulator,
various connected graphs, in which vertices and edges represent atoms and
blockaded couplings, respectively, are constructed in two or three-dimensional
space and their eigenenergies are probed during their topological
transformations. Star, complete, cyclic, and diamond graphs, and their
geometric intermediates, are tested for four atoms and antiprism structures for
six atoms. Spectroscopic resolution (dE/E) less than 10% is achieved and the
observed energy level shifts and merges through structural transformations are
in good agreement with the model few-body quantum-Ising Hamiltonian.Comment: 8 pages, 4 figure
Quantum annealing of Cayley-tree Ising spins at small scales
Significant efforts are being directed towards developing a quantum annealer
capable of solving combinatorial optimization problems. The challenges are
Hamiltonian programming and large-scale implementations. Here we report quantum
annealing demonstration of Ising Hamiltonians programmed with up to
spins mapped on various Cayley tree graphs. Experiments are performed with a
Rydberg-atom quantum simulator, in which rubidium single atoms are arranged in
three dimensional space in such a way that their Rydberg atoms and blockaded
strong couplings respectively represent the nodes and edges of each graph.
Three different Cayley-tree graphs of neighbors and of up to shells
are constructed, and their ground-state phases and N\'{e}el's order formations
are probed. In good agreement with model calculations, the anti-ferromagnetic
phase in regular Cayley trees and frustrated competing ground-states in a
dual-center Cayley tree are directly observed. This demonstrates the
possibilities of high-dimensional qubit connection programming in quantum
simulators.Comment: 7 pages,5 figure