126 research outputs found
Quantum Measurement and the Aharonov-Bohm Effect with Superposed Magnetic Fluxes
We consider the magnetic flux in a quantum mechanical superposition of two
values and find that the Aharonov-Bohm effect interference pattern contains
information about the nature of the superposition, allowing information about
the state of the flux to be extracted without disturbance. The information is
obtained without transfer of energy or momentum and by accumulated nonlocal
interactions of the vector potential with many charged particles
forming the interference pattern, rather than with a single particle. We
suggest an experimental test using already experimentally realized superposed
currents in a superconducting ring and discuss broader implications.Comment: 6 pages, 4 figures; Changes from version 3: corrected typo (not
present in versions 1 and 2) in Eq. 8; Changes from version 2: shortened
abstract; added refs and material in Section IV. The final publication is
available at: http://link.springer.com/article/10.1007/s11128-013-0652-
Experimental demonstration of quantum memory for light
The information carrier of today's communications, a weak pulse of light, is
an intrinsically quantum object. As a consequence, complete information about
the pulse cannot, even in principle, be perfectly recorded in a classical
memory. In the field of quantum information this has led to a long standing
challenge: how to achieve a high-fidelity transfer of an independently prepared
quantum state of light onto the atomic quantum state? Here we propose and
experimentally demonstrate a protocol for such quantum memory based on atomic
ensembles. We demonstrate for the first time a recording of an externally
provided quantum state of light onto the atomic quantum memory with a fidelity
up to 70%, significantly higher than that for the classical recording. Quantum
storage of light is achieved in three steps: an interaction of light with
atoms, the subsequent measurement on the transmitted light, and the feedback
onto the atoms conditioned on the measurement result. Density of recorded
states 33% higher than that for the best classical recording of light on atoms
is achieved. A quantum memory lifetime of up to 4 msec is demonstrated.Comment: 22 pages (double line spacing) incl. supplementary information, 4
figures, accepted for publication in Natur
Topologically protected quantum bits from Josephson junction arrays
All physical implementations of quantum bits (qubits), carrying the
information and computation in a putative quantum computer, have to meet the
conflicting requirements of environmental decoupling while remaining
manipulable through designed external signals. Proposals based on quantum
optics naturally emphasize the aspect of optimal isolation, while those
following the solid state route exploit the variability and scalability of
modern nanoscale fabrication techniques. Recently, various designs using
superconducting structures have been successfully tested for quantum coherent
operation, however, the ultimate goal of reaching coherent evolution over
thousands of elementary operations remains a formidable task. Protecting qubits
from decoherence by exploiting topological stability, a qualitatively new
proposal due to Kitaev, holds the promise for long decoherence times, but its
practical physical implementation has remained unclear so far. Here, we show
how strongly correlated systems developing an isolated two-fold degenerate
quantum dimer liquid groundstate can be used in the construction of
topologically stable qubits and discuss their implementation using Josephson
junction arrays.Comment: 6 pages, 4 figure
Quantum oscillations in two coupled charge qubits
Despite an apparent progress in implementing individual solid-state qubits,
there have been no experimental reports so far on multi-bit gates required for
building a real quantum computer. Here we report a new circuit comprising two
coupled charge qubits. Using a pulse technique, we coherently mix quantum
states and observe quantum oscillations whose spectrum reflects interaction
between the qubits. Our results demonstrate the feasibility of coupling of
multiple solid-state qubits and indicate the existence of entangled two-qubit
states.Comment: 4 pages, 4 figures, submitted to Natur
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
Coding on countably infinite alphabets
This paper describes universal lossless coding strategies for compressing
sources on countably infinite alphabets. Classes of memoryless sources defined
by an envelope condition on the marginal distribution provide benchmarks for
coding techniques originating from the theory of universal coding over finite
alphabets. We prove general upper-bounds on minimax regret and lower-bounds on
minimax redundancy for such source classes. The general upper bounds emphasize
the role of the Normalized Maximum Likelihood codes with respect to minimax
regret in the infinite alphabet context. Lower bounds are derived by tailoring
sharp bounds on the redundancy of Krichevsky-Trofimov coders for sources over
finite alphabets. Up to logarithmic (resp. constant) factors the bounds are
matching for source classes defined by algebraically declining (resp.
exponentially vanishing) envelopes. Effective and (almost) adaptive coding
techniques are described for the collection of source classes defined by
algebraically vanishing envelopes. Those results extend ourknowledge concerning
universal coding to contexts where the key tools from parametric inferenceComment: 33 page
Ipsilateral common iliac artery plus femoral artery clamping for inducing sciatic nerve ischemia/reperfusion injury in rats: a reliable and simple method
The aim of this study was to develop a practical model of sciatic ischemia reperfusion (I/R) injury producing serious neurologic deficits and being technically feasible compared with the current time consuming or ineffective models. Thirty rats were divided into 6 groups (n = 5). Animal were anesthetized by using ketamine (50 mg/kg) and xylazine (4 mg/kg). Experimental groups included a sham-operated group and five I/R groups with different reperfusion time intervals (0 h, 3 h, 1 d, 4 d, 7 d). In I/R groups, the right common iliac artery and the right femoral artery were clamped for 3 hrs. Sham-operated animals underwent only laparotomy without induction of ischemia. Just before euthanasia, behavioral scores (based on gait, grasp, paw position, and pinch sensitivity) were obtained and then sciatic nerves were removed for light-microscopy studies (for ischemic fiber degeneration (IFD) and edema). Behavioral score deteriorated among the ischemic groups compared with the control group (p < 0.01), with maximal behavioral deficit occurring at 4 days of reperfusion. Axonal swelling and IFD were found to happen only after 4 and 7 days, respectively. Our observations led to an easy-to-use but strong enough method for inducing and studying I/R injury in peripheral nerves
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
The phosphatase and tensin homologue deleted on chromosome 10 mediates radiosensitivity in head and neck cancer
BACKGROUND: For locally advanced squamous cell carcinoma of the head and neck (HNSCC), the recurrence rate after surgery and postoperative radiotherapy is between 20 and 40%, and the 5- year overall survival rate is similar to 50%. Presently, no markers exist to accurately predict treatment outcome. Expression of proteins in the human epidermal growth factor receptor (EGFR) pathway has been reported as a prognostic marker in several types of cancer. METHODS: The aim of this study was to investigate the prognostic value of proteins in the EGFR pathway in HNSCC. For this purpose, we collected surgically resected tissue of 140 locally advanced head and neck cancer patients, all treated with surgery and postoperative radiotherapy. RESULTS: In a multivariate analysis, expression of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) was significantly related to worse locoregional control (LRC; HR: 2.2, 95% CI: 1.1-4.6; P = 0.03), independent of lymph node metastases (HR: 5.6, 95% CI: 1.2-27.4; P = 0.03) and extranodal spread (HR: 2.7; 95% CI: 1.2- 6.5; P = 0.02). In vitro clonogenic radiosensitivity assays confirmed that overexpression of PTEN resulted in increased radioresistance. CONCLUSION: Our study is the first report showing that expression of PTEN mediates radiosensitivity in vitro and that increased expression in advanced HNSCC predicts worse LRC. British Journal of Cancer (2010) 102, 1778-1785. doi: 10.1038/sj.bjc.6605707 www.bjcancer.com Published online 25 May 2010 (C) 2010 Cancer Research U
Amplitude Spectroscopy of a Solid-State Artificial Atom
The energy-level structure of a quantum system plays a fundamental role in
determining its behavior and manifests itself in a discrete absorption and
emission spectrum. Conventionally, spectra are probed via frequency
spectroscopy whereby the frequency \nu of a harmonic driving field is varied to
fulfill the conditions \Delta E = h \nu, where the driving field is resonant
with the level separation \Delta E (h is Planck's constant). Although this
technique has been successfully employed in a variety of physical systems,
including natural and artificial atoms and molecules, its application is not
universally straightforward, and becomes extremely challenging for frequencies
in the range of 10's and 100's of gigahertz. Here we demonstrate an alternative
approach, whereby a harmonic driving field sweeps the atom through its
energy-level avoided crossings at a fixed frequency, surmounting many of the
limitations of the conventional approach. Spectroscopic information is obtained
from the amplitude dependence of the system response. The resulting
``spectroscopy diamonds'' contain interference patterns and population
inversion that serve as a fingerprint of the atom's spectrum. By analyzing
these features, we determine the energy spectrum of a manifold of states with
energies from 0.01 to 120 GHz \times h in a superconducting artificial atom,
using a driving frequency near 0.1 GHz. This approach provides a means to
manipulate and characterize systems over a broad bandwidth, using only a single
driving frequency that may be orders of magnitude smaller than the energy
scales being probed.Comment: 12 pages, 13 figure
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