388 research outputs found
Theory of Photon Blockade by an Optical Cavity with One Trapped Atom
In our recent paper [1], we reported observations of photon blockade by one
atom strongly coupled to an optical cavity. In support of these measurements,
here we provide an expanded discussion of the general phenomenology of photon
blockade as well as of the theoretical model and results that were presented in
Ref. [1]. We describe the general condition for photon blockade in terms of the
transmission coefficients for photon number states. For the atom-cavity system
of Ref. [1], we present the model Hamiltonian and examine the relationship of
the eigenvalues to the predicted intensity correlation function. We explore the
effect of different driving mechanisms on the photon statistics. We also
present additional corrections to the model to describe cavity birefringence
and ac-Stark shifts. [1] K. M. Birnbaum, A. Boca, R. Miller, A. D. Boozer, T.
E. Northup, and H. J. Kimble, Nature 436, 87 (2005).Comment: 10 pages, 6 figure
Entanglement of spin waves among four quantum memories
Quantum networks are composed of quantum nodes that interact coherently by
way of quantum channels and open a broad frontier of scientific opportunities.
For example, a quantum network can serve as a `web' for connecting quantum
processors for computation and communication, as well as a `simulator' for
enabling investigations of quantum critical phenomena arising from interactions
among the nodes mediated by the channels. The physical realization of quantum
networks generically requires dynamical systems capable of generating and
storing entangled states among multiple quantum memories, and of efficiently
transferring stored entanglement into quantum channels for distribution across
the network. While such capabilities have been demonstrated for diverse
bipartite systems (i.e., N=2 quantum systems), entangled states with N > 2 have
heretofore not been achieved for quantum interconnects that coherently `clock'
multipartite entanglement stored in quantum memories to quantum channels. Here,
we demonstrate high-fidelity measurement-induced entanglement stored in four
atomic memories; user-controlled, coherent transfer of atomic entanglement to
four photonic quantum channels; and the characterization of the full
quadripartite entanglement by way of quantum uncertainty relations. Our work
thereby provides an important tool for the distribution of multipartite
entanglement across quantum networks.Comment: 4 figure
Interfacing External Quantum Devices to a Universal Quantum Computer
We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantum computers. We show how to accomplish this by devising universal quantum computer programs that implement well known oracle based quantum algorithms, namely the Deutsch, Deutsch-Jozsa, and the Grover algorithms using external black-box quantum oracle devices. In the process, we demonstrate a method to map existing quantum algorithms onto the universal quantum computer
Predicting Phenotypic Diversity and the Underlying Quantitative Molecular Transitions
During development, signaling networks control the formation of multicellular patterns. To what extent quantitative fluctuations in these complex networks may affect multicellular phenotype remains unclear. Here, we describe a computational approach to predict and analyze the phenotypic diversity that is accessible to a developmental signaling network. Applying this framework to vulval development in C. elegans, we demonstrate that quantitative changes in the regulatory network can render ~500 multicellular phenotypes. This phenotypic capacity is an order-of-magnitude below the theoretical upper limit for this system but yet is large enough to demonstrate that the system is not restricted to a select few outcomes. Using metrics to gauge the robustness of these phenotypes to parameter perturbations, we identify a select subset of novel phenotypes that are the most promising for experimental validation. In addition, our model calculations provide a layout of these phenotypes in network parameter space. Analyzing this landscape of multicellular phenotypes yielded two significant insights. First, we show that experimentally well-established mutant phenotypes may be rendered using non-canonical network perturbations. Second, we show that the predicted multicellular patterns include not only those observed in C. elegans, but also those occurring exclusively in other species of the Caenorhabditis genus. This result demonstrates that quantitative diversification of a common regulatory network is indeed demonstrably sufficient to generate the phenotypic differences observed across three major species within the Caenorhabditis genus. Using our computational framework, we systematically identify the quantitative changes that may have occurred in the regulatory network during the evolution of these species. Our model predictions show that significant phenotypic diversity may be sampled through quantitative variations in the regulatory network without overhauling the core network architecture. Furthermore, by comparing the predicted landscape of phenotypes to multicellular patterns that have been experimentally observed across multiple species, we systematically trace the quantitative regulatory changes that may have occurred during the evolution of the Caenorhabditis genus
Motional sidebands and direct measurement of the cooling rate in the resonance fluorescence of a single trapped ion
Resonance fluorescence of a single trapped ion is spectrally analyzed using a
heterodyne technique. Motional sidebands due to the oscillation of the ion in
the harmonic trap potential are observed in the fluorescence spectrum. From the
width of the sidebands the cooling rate is obtained and found to be in
agreement with the theoretical prediction.Comment: 4 pages, 4 figures. Final version after minor changes, 1 figure
replaced; to be published in PRL, July 10, 200
Measurements of the Correlation Function of a Microwave Frequency Single Photon Source
At optical frequencies the radiation produced by a source, such as a laser, a
black body or a single photon source, is frequently characterized by analyzing
the temporal correlations of emitted photons using single photon counters. At
microwave frequencies, however, there are no efficient single photon counters
yet. Instead, well developed linear amplifiers allow for efficient measurement
of the amplitude of an electromagnetic field. Here, we demonstrate how the
properties of a microwave single photon source can be characterized using
correlation measurements of the emitted radiation with such detectors. We also
demonstrate the cooling of a thermal field stored in a cavity, an effect which
we detect using a cross-correlation measurement of the radiation emitted at the
two ends of the cavity.Comment: 5 pages, 4 figure
Measurement-Induced Entanglement for Excitation Stored in Remote Atomic Ensembles
A critical requirement for diverse applications in Quantum Information
Science is the capability to disseminate quantum resources over complex quantum
networks. For example, the coherent distribution of entangled quantum states
together with quantum memory to store these states can enable scalable
architectures for quantum computation, communication, and metrology. As a
significant step toward such possibilities, here we report observations of
entanglement between two atomic ensembles located in distinct apparatuses on
different tables. Quantum interference in the detection of a photon emitted by
one of the samples projects the otherwise independent ensembles into an
entangled state with one joint excitation stored remotely in 10^5 atoms at each
site. After a programmable delay, we confirm entanglement by mapping the state
of the atoms to optical fields and by measuring mutual coherences and photon
statistics for these fields. We thereby determine a quantitative lower bound
for the entanglement of the joint state of the ensembles. Our observations
provide a new capability for the distribution and storage of entangled quantum
states, including for scalable quantum communication networks .Comment: 13 pages, 4 figures Submitted for publication on August 31 200
Conditional control of the quantum states of remote atomic memories for quantum networking
Quantum networks hold the promise for revolutionary advances in information
processing with quantum resources distributed over remote locations via
quantum-repeater architectures. Quantum networks are composed of nodes for
storing and processing quantum states, and of channels for transmitting states
between them. The scalability of such networks relies critically on the ability
to perform conditional operations on states stored in separated quantum
memories. Here we report the first implementation of such conditional control
of two atomic memories, located in distinct apparatuses, which results in a
28-fold increase of the probability of simultaneously obtaining a pair of
single photons, relative to the case without conditional control. As a first
application, we demonstrate a high degree of indistinguishability for remotely
generated single photons by the observation of destructive interference of
their wavepackets. Our results demonstrate experimentally a basic principle for
enabling scalable quantum networks, with applications as well to linear optics
quantum computation.Comment: 10 pages, 8 figures; Minor corrections. References updated. Published
at Nature Physics 2, Advanced Online Publication of 10/29 (2006
Heralded quantum entanglement between two crystals
Quantum networks require the crucial ability to entangle quantum nodes. A
prominent example is the quantum repeater which allows overcoming the distance
barrier of direct transmission of single photons, provided remote quantum
memories can be entangled in a heralded fashion. Here we report the observation
of heralded entanglement between two ensembles of rare-earth-ions doped into
separate crystals. A heralded single photon is sent through a 50/50
beamsplitter, creating a single-photon entangled state delocalized between two
spatial modes. The quantum state of each mode is subsequently mapped onto a
crystal, leading to an entangled state consisting of a single collective
excitation delocalized between two crystals. This entanglement is revealed by
mapping it back to optical modes and by estimating the concurrence of the
retrieved light state. Our results highlight the potential of rare-earth-ions
doped crystals for entangled quantum nodes and bring quantum networks based on
solid-state resources one step closer.Comment: 10 pages, 5 figure
Quantum teleportation using active feed-forward between two Canary Islands
Quantum teleportation [1] is a quintessential prerequisite of many quantum
information processing protocols [2-4]. By using quantum teleportation, one can
circumvent the no-cloning theorem [5] and faithfully transfer unknown quantum
states to a party whose location is even unknown over arbitrary distances. Ever
since the first experimental demonstrations of quantum teleportation of
independent qubits [6] and of squeezed states [7], researchers have
progressively extended the communication distance in teleportation, usually
without active feed-forward of the classical Bell-state measurement result
which is an essential ingredient in future applications such as communication
between quantum computers. Here we report the first long-distance quantum
teleportation experiment with active feed-forward in real time. The experiment
employed two optical links, quantum and classical, over 143 km free space
between the two Canary Islands of La Palma and Tenerife. To achieve this, the
experiment had to employ novel techniques such as a frequency-uncorrelated
polarization-entangled photon pair source, ultra-low-noise single-photon
detectors, and entanglement-assisted clock synchronization. The average
teleported state fidelity was well beyond the classical limit of 2/3.
Furthermore, we confirmed the quality of the quantum teleportation procedure
(without feed-forward) by complete quantum process tomography. Our experiment
confirms the maturity and applicability of the involved technologies in
real-world scenarios, and is a milestone towards future satellite-based quantum
teleportation
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