138 research outputs found
A heralded quantum gate between remote quantum memories
We demonstrate a probabilistic entangling quantum gate between two distant
trapped ytterbium ions. The gate is implemented between the hyperfine "clock"
state atomic qubits and mediated by the interference of two emitted photons
carrying frequency encoded qubits. Heralded by the coincidence detection of
these two photons, the gate has an average fidelity of 90+-2%. This entangling
gate together with single qubit operations is sufficient to generate large
entangled cluster states for scalable quantum computing
General limit to non-destructive optical detection of atoms
We demonstrate that there is a fundamental limit to the sensitivity of
phase-based detection of atoms with light for a given maximum level of
allowable spontaneous emission. This is a generalisation of previous results
for two-level and three-level atoms. The limit is due to an upper bound on the
phase shift that can be imparted on a laser beam for a given excited state
population. Specifially, we show that no single-pass optical technique using
classical light, based on any number of lasers or coherences between any number
of levels, can exceed the limit imposed by the two-level atom. This puts
significant restrictions on potential non-destructive optical measurement
schemes.Comment: 7 pages, 1 figur
Manipulation and Detection of a Trapped Yb+ Ion Hyperfine Qubit
We demonstrate the use of trapped ytterbium ions as quantum bits for quantum
information processing. We implement fast, efficient state preparation and
state detection of the first-order magnetic field-insensitive hyperfine levels
of 171Yb+, with a measured coherence time of 2.5 seconds. The high efficiency
and high fidelity of these operations is accomplished through the stabilization
and frequency modulation of relevant laser sources.Comment: 10 pages, 9 figures, 1 tabl
Distributed Quantum Computation Based-on Small Quantum Registers
We describe and analyze an efficient register-based hybrid quantum
computation scheme. Our scheme is based on probabilistic, heralded optical
connection among local five-qubit quantum registers. We assume high fidelity
local unitary operations within each register, but the error probability for
initialization, measurement, and entanglement generation can be very high
(~5%). We demonstrate that with a reasonable time overhead our scheme can
achieve deterministic non-local coupling gates between arbitrary two registers
with very high fidelity, limited only by the imperfections from the local
unitary operation. We estimate the clock cycle and the effective error
probability for implementation of quantum registers with ion-traps or
nitrogen-vacancy (NV) centers. Our new scheme capitalizes on a new efficient
two-level pumping scheme that in principle can create Bell pairs with
arbitrarily high fidelity. We introduce a Markov chain model to study the
stochastic process of entanglement pumping and map it to a deterministic
process. Finally we discuss requirements for achieving fault-tolerant operation
with our register-based hybrid scheme, and also present an alternative approach
to fault-tolerant preparation of GHZ states.Comment: 22 Pages, 23 Figures and 1 Table (updated references
Entanglement of Atomic Qubits using an Optical Frequency Comb
We demonstrate the use of an optical frequency comb to coherently control and
entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used
to efficiently and coherently transfer population between electronic and
vibrational states of trapped atomic ions and implement an entangling quantum
logic gate with high fidelity. This technique can be extended to the high field
regime where operations can be performed faster than the trap frequency. This
general approach can be applied to more complex quantum systems, such as large
collections of interacting atoms or molecules.Comment: 4 pages, 5 figure
Quantum Teleportation Between Distant Matter Qubits
Quantum teleportation is the faithful transfer of quantum states between
systems, relying on the prior establishment of entanglement and using only
classical communication during the transmission. We report teleportation of
quantum information between atomic quantum memories separated by about 1 meter.
A quantum bit stored in a single trapped ytterbium ion (Yb+) is teleported to a
second Yb+ atom with an average fidelity of 90% over a replete set of states.
The teleportation protocol is based on the heralded entanglement of the atoms
through interference and detection of photons emitted from each atom and guided
through optical fibers. This scheme may be used for scalable quantum
computation and quantum communication.Comment: 5 pages, 4 figure
Jaynes-Cummings Models with trapped surface-state electrons in THz cavities
An electron floating on the liquid Helium is proposed to be trapped (by a
micro-electrode set below the liquid Helium) in a high finesse cavity. Two
lowest levels of the vertical motion of the electron acts as a two-level
"atom", which could resonantly interact with the THz cavity. In the Lamb-Dicke
regime, wherein the electron's in-plane activity region is much smaller than
the wavelength of the cavity mode, the famous Jaynes-Cummings model (JCM) could
be realized. By applying an additional external classical laser beam to the
electron, a driven JCM could also be implemented. With such a driven JCM
certain quantum states, e.g., coherent states and the Schrodinger cat states,
of the THz cavity field could be prepared by one-step evolution. The numerical
results show that, for the typical parameters of the cavity and electron on
liquid Helium, a strong coupling between the artificial atom and the THz cavity
could be obtained.Comment: 11 pages, 1 figure
Vacuum-stimulated cooling of single atoms in three dimensions
Taming quantum dynamical processes is the key to novel applications of
quantum physics, e.g. in quantum information science. The control of
light-matter interactions at the single-atom and single-photon level can be
achieved in cavity quantum electrodynamics, in particular in the regime of
strong coupling where atom and cavity form a single entity. In the optical
domain, this requires permanent trapping and cooling of an atom in a
micro-cavity. We have now realized three-dimensional cavity cooling and
trapping for an orthogonal arrangement of cooling laser, trap laser and cavity
vacuum. This leads to average single-atom trapping times exceeding 15 seconds,
unprecedented for a strongly coupled atom under permanent observation.Comment: 4 pages, 4 figure
Entanglement of two interacting bosons in a two dimensional isotropic harmonic trap
We compute the pair entanglement between two interacting bosons in a two
dimensional (2D)isotropic harmonic trap. The interaction potential is modeled
by a 2D regularized pseudo-potential. By analytically decomposing the wave
function into the single particle basis, we show the dependency of the pair
entanglement on the scattering length. Our results turn out to be in good
agreements with earlier results using a quasi-2D geometry.Comment: 5 figure
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