281 research outputs found
The Quantum Internet
Quantum networks offer a unifying set of opportunities and challenges across
exciting intellectual and technical frontiers, including for quantum
computation, communication, and metrology. The realization of quantum networks
composed of many nodes and channels requires new scientific capabilities for
the generation and characterization of quantum coherence and entanglement.
Fundamental to this endeavor are quantum interconnects that convert quantum
states from one physical system to those of another in a reversible fashion.
Such quantum connectivity for networks can be achieved by optical interactions
of single photons and atoms, thereby enabling entanglement distribution and
quantum teleportation between nodes.Comment: 15 pages, 6 figures Higher resolution versions of the figures can be
downloaded from the following link:
http://www.its.caltech.edu/~hjkimble/QNet-figures-high-resolutio
Measuring Nothing
Measurement is integral to quantum information processing and communication;
it is how information encoded in the state of a system is transformed into
classical signals for further use. In quantum optics, measurements are
typically destructive, so that the state is not available afterwards for
further steps - crucial for sequential measurement schemes. The development of
practical methods for non-destructive measurements on optical fields is
therefore an important topic for future practical quantum information
processing systems. Here we show how to measure the presence or absence of the
vacuum in a quantum optical field without destroying the state, implementing
the ideal projections onto the respective subspaces. This not only enables
sequential measurements, useful for quantum communication, but it can also be
adapted to create novel states of light via bare raising and lowering
operators.Comment: 7 pages, 4 figure
Telecom photon interface of solid-state quantum nodes
Solid-state spins such as nitrogen-vacancy (NV) center are promising
platforms for large-scale quantum networks. Despite the optical interface of NV
center system, however, the significant attenuation of its zero-phonon-line
photon in optical fiber prevents the network extended to long distances.
Therefore a telecom-wavelength photon interface would be essential to reduce
the photon loss in transporting quantum information. Here we propose an
efficient scheme for coupling telecom photon to NV center ensembles mediated by
rare-earth doped crystal. Specifically, we proposed protocols for high fidelity
quantum state transfer and entanglement generation with parameters within reach
of current technologies. Such an interface would bring new insights into future
implementations of long-range quantum network with NV centers in diamond acting
as quantum nodes.Comment: 10 pages, 5 figure
Dynamic generation of maximally entangled photon multiplets by adiabatic passage
The adiabatic passage scheme for quantum state synthesis, in which atomic
Zeeman coherences are mapped to photon states in an optical cavity, is extended
to the general case of two degenerate cavity modes with orthogonal
polarization. Analytical calculations of the dressed-state structure and Monte
Carlo wave-function simulations of the system dynamics show that, for a
suitably chosen cavity detuning, it is possible to generate states of photon
multiplets that are maximally entangled in polarization. These states display
nonclassical correlations of the type described by Greenberger, Horne, and
Zeilinger (GHZ). An experimental scheme to realize a GHZ measurement using
coincidence detection of the photons escaping from the cavity is proposed. The
correlations are found to originate in the dynamics of the adiabatic passage
and persist even if cavity decay and GHZ state synthesis compete on the same
time scale. Beyond entangled field states, it is also possible to generate
entanglement between photons and the atom by using a different atomic
transition and initial Zeeman state.Comment: 22 pages (RevTeX), including 23 postscript figures. To be published
in Physical Review
A non-adiabatic approach to entanglement distribution over long distances
Entanglement distribution between trapped-atom quantum memories, viz. single
atoms in optical cavities, is addressed. In most scenarios, the rate of
entanglement distribution depends on the efficiency with which the state of
traveling single photons can be transferred to trapped atoms. This loading
efficiency is analytically studied for two-level, -level, -level,
and double--level atomic configurations by means of a system-reservoir
approach. An off-resonant non-adiabatic approach to loading -level
trapped-atom memories is proposed, and the ensuing trade-offs between the
atom-light coupling rate and input photon bandwidth for achieving a high
loading probability are identified. The non-adiabatic approach allows a broad
class of optical sources to be used, and in some cases it provides a higher
system throughput than what can be achieved by adiabatic loading mechanisms.
The analysis is extended to the case of two double- trapped-atom
memories illuminated by a polarization-entangled biphoton.Comment: 15 pages, 15 figure
An Elementary Quantum Network of Single Atoms in Optical Cavities
Quantum networks are distributed quantum many-body systems with tailored
topology and controlled information exchange. They are the backbone of
distributed quantum computing architectures and quantum communication. Here we
present a prototype of such a quantum network based on single atoms embedded in
optical cavities. We show that atom-cavity systems form universal nodes capable
of sending, receiving, storing and releasing photonic quantum information.
Quantum connectivity between nodes is achieved in the conceptually most
fundamental way: by the coherent exchange of a single photon. We demonstrate
the faithful transfer of an atomic quantum state and the creation of
entanglement between two identical nodes in independent laboratories. The
created nonlocal state is manipulated by local qubit rotation. This efficient
cavity-based approach to quantum networking is particularly promising as it
offers a clear perspective for scalability, thus paving the way towards
large-scale quantum networks and their applications.Comment: 8 pages, 5 figure
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