107 research outputs found
Quantum Key Distribution over Probabilistic Quantum Repeaters
A feasible route towards implementing long-distance quantum key distribution
(QKD) systems relies on probabilistic schemes for entanglement distribution and
swapping as proposed in the work of Duan, Lukin, Cirac, and Zoller (DLCZ)
[Nature 414, 413 (2001)]. Here, we calculate the conditional throughput and
fidelity of entanglement for DLCZ quantum repeaters, by accounting for the DLCZ
self-purification property, in the presence of multiple excitations in the
ensemble memories as well as loss and other sources of inefficiency in the
channel and measurement modules. We then use our results to find the generation
rate of secure key bits for QKD systems that rely on DLCZ quantum repeaters. We
compare the key generation rate per logical memory employed in the two cases of
with and without a repeater node. We find the cross-over distance beyond which
the repeater system outperforms the non-repeater one. That provides us with the
optimum inter-node distancing in quantum repeater systems. We also find the
optimal excitation probability at which the QKD rate peaks. Such an optimum
probability, in most regimes of interest, is insensitive to the total distance.Comment: 12 pages, 6 figures; Fig. 5(a) is replace
Cavity sideband cooling of a single trapped ion
We report a demonstration and quantitative characterization of
one-dimensional cavity cooling of a single trapped 88Sr+ ion in the resolved
sideband regime. We measure the spectrum of cavity transitions, the rates of
cavity heating and cooling, and the steady-state cooling limit. The cavity
cooling dynamics and cooling limit of 22.5(3) motional quanta, limited by the
moderate coupling between the ion and the cavity, are consistent with a simple
model [Phys. Rev. A 64, 033405] without any free parameters, validating the
rate equation model for cavity cooling.Comment: 5 pages, 4 figure
Quantum interface between an electrical circuit and a single atom
We show how to bridge the divide between atomic systems and electronic
devices by engineering a coupling between the motion of a single ion and the
quantized electric field of a resonant circuit. Our method can be used to
couple the internal state of an ion to the quantized circuit with the same
speed as the internal-state coupling between two ions. All the well-known
quantum information protocols linking ion internal and motional states can be
converted to protocols between circuit photons and ion internal states. Our
results enable quantum interfaces between solid state qubits, atomic qubits,
and light, and lay the groundwork for a direct quantum connection between
electrical and atomic metrology standards.Comment: Supplemental material available on reques
Relating Green's Functions in Axial and Lorentz Gauges using Finite Field-Dependent BRS Transformations
We use finite field-dependent BRS transformations (FFBRS) to connect the
Green functions in a set of two otherwise unrelated gauge choices. We choose
the Lorentz and the axial gauges as examples. We show how the Green functions
in axial gauge can be written as a series in terms of those in Lorentz gauges.
Our method also applies to operator Green's functions. We show that this
process involves another set of related FFBRS transfomations that is derivable
from infinitesimal FBRS. We suggest possible applications.Comment: 20 pages, LaTex, Section 4 expanded, typos corrected; last 2
references modified; (this) revised version to appear in J. Math. Phy
Ion traps fabricated in a CMOS foundry
We demonstrate trapping in a surface-electrode ion trap fabricated in a 90-nm
CMOS (complementary metal-oxide-semiconductor) foundry process utilizing the
top metal layer of the process for the trap electrodes. The process includes
doped active regions and metal interconnect layers, allowing for co-fabrication
of standard CMOS circuitry as well as devices for optical control and
measurement. With one of the interconnect layers defining a ground plane
between the trap electrode layer and the p-type doped silicon substrate, ion
loading is robust and trapping is stable. We measure a motional heating rate
comparable to those seen in surface-electrode traps of similar size. This is
the first demonstration of scalable quantum computing hardware, in any
modality, utilizing a commercial CMOS process, and it opens the door to
integration and co-fabrication of electronics and photonics for large-scale
quantum processing in trapped-ion arrays.Comment: 4 pages, 3 figure
Cryogenic Ion Trapping Systems with Surface-Electrode Traps
We present two simple cryogenic RF ion trap systems in which cryogenic
temperatures and ultra high vacuum pressures can be reached in as little as 12
hours. The ion traps are operated either in a liquid helium bath cryostat or in
a low vibration closed cycle cryostat. The fast turn around time and
availability of buffer gas cooling made the systems ideal for testing
surface-electrode ion traps. The vibration amplitude of the closed cycled
cryostat was found to be below 106 nm. We evaluated the systems by loading
surface-electrode ion traps with Sr ions using laser ablation, which
is compatible with the cryogenic environment. Using Doppler cooling we observed
small ion crystals in which optically resolved ions have a trapped lifetime
over 2500 minutes.Comment: 10 pages, 13 EPS figure
Superconducting microfabricated ion traps
We fabricate superconducting ion traps with niobium and niobium nitride and
trap single 88Sr ions at cryogenic temperatures. The superconducting transition
is verified and characterized by measuring the resistance and critical current
using a 4-wire measurement on the trap structure, and observing change in the
rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz
at 6 K and shows no significant change across the superconducting transition,
suggesting that anomalous heating is primarily caused by noise sources on the
surface. This demonstration of superconducting ion traps opens up possibilities
for integrating trapped ions and molecular ions with superconducting devices.Comment: 3 pages, 2 figure
Sympathetic Cooling of Mixed Species Two-Ion Crystals for Precision Spectroscopy
Sympathetic cooling of trapped ions has become an indispensable tool for
quantum information processing and precision spectroscopy. In the simplest
situation a single Doppler-cooled ion sympathetically cools another ion which
typically has a different mass. We analytically investigate the effect of the
mass ratio of such an ion crystal on the achievable temperature limit in the
presence of external heating. As an example, we show that cooling of a single
Al+ with Be+, Mg+ and Ca+ ions provides similar results for heating rates
typically observed in ion traps, whereas cooling ions with a larger mass
perform worse. Furthermore, we present numerical simulation results of the
rethermalisation dynamics after a background gas collision for the Al+/Ca+
crystal for different cooling laser configurations.Comment: Made Graphics black & white print compatible, clarified abstract and
summar
Suppression of Heating Rates in Cryogenic Surface-Electrode Ion Traps
Dense arrays of trapped ions provide one way of scaling up ion trap quantum
information processing. However, miniaturization of ion traps is currently
limited by sharply increasing motional state decoherence at sub-100 um
ion-electrode distances. We characterize heating rates in cryogenically cooled
surface-electrode traps, with characteristic sizes in 75 um to 150 um range.
Upon cooling to 6 K, the measured rates are suppressed by 7 orders of
magnitude, two orders of magnitude below previously published data of similarly
sized traps operated at room temperature. The observed noise depends strongly
on fabrication process, which suggests further improvements are possible.Comment: 4 pages, 4 figure
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