924 research outputs found
Decoherence in a Josephson junction qubit
The zero-voltage state of a Josephson junction biased with constant current
consists of a set of metastable quantum energy levels. We probe the spacings of
these levels by using microwave spectroscopy to enhance the escape rate to the
voltage state. The widths of the resonances give a measurement of the coherence
time of the two states involved in the transitions. We observe a decoherence
time shorter than that expected from dissipation alone in resonantly isolated
20 um x 5 um Al/AlOx/Al junctions at 60 mK. The data is well fit by a model
including dephasing effects of both low-frequency current noise and the escape
rate to the continuum voltage states. We discuss implications for quantum
computation using current-biased Josephson junction qubits, including the
minimum number of levels needed in the well to obtain an acceptable error limit
per gate.Comment: 4 pages, 6 figure
Charge and Isospin Fluctuations in High Energy pp-Collisions
Charge and isospin event-by-event fluctuations in high-energy pp-collisions
are predicted within the Unitary Eikonal Model, in particular the fluctuation
patterns of the ratios of charged-to-charged and neutral-to-charged pions.
These fluctuations are found to be sensitive to the presence of unstable
resonances, such as and mesons. We predict that the
charge-fluctuation observable should be restricted to the interval
depending on the production ratio. Also, the
isospin fluctuations of the DCC-type of the ratio of neutral-to-charged pions
are suppressed if pions are produced together with mesons.Comment: Latex, 5 pages, no figures. To appear in the proceedings of 9th
Adriatic Meeting, Dubrovnik, Croatia, 4 - 14 September 2003. Added reference
into reference no.
Cancer Vaccines: From the State of the Art to the Most Promising Frontiers in the Treatment of Colorectal Cancer
Colorectal cancer represents 10% of all new cancer cases each year and accounts for almost 10% of all cancer deaths. According to the WHO, by 2040 there will be a 60% increase in colorectal cancer cases. These data highlight the need to explore new therapeutic strategies. Classical interventions include surgical resection, chemotherapy and radiotherapy, which are invasive strategies that have many side effects on the patients and greatly affect their quality of life. A great advance in the treatment of this cancer type, as well as of all the others, could be the development of a vaccination strategy preventing the onset, the progression or the relapse of the pathology. In this review, we summarize the main vaccination strategies that are being studied for the treatment of colorectal cancer (CRC) and finally explore the possibility of using B-cells for the development of a new type of vaccine
Observation of quantum oscillations between a Josephson phase qubit and a microscopic resonator using fast readout
We have detected coherent quantum oscillations between Josephson phase qubits
and microscopic critical-current fluctuators by implementing a new state
readout technique that is an order of magnitude faster than previous methods.
The period of the oscillations is consistent with the spectroscopic splittings
observed in the qubit's resonant frequency. The results point to a possible
mechanism for decoherence and reduced measurement fidelity in superconducting
qubits and demonstrate the means to measure two-qubit interactions in the time
domain
State tomography of capacitively shunted phase qubits with high fidelity
We introduce a new design concept for superconducting quantum bits (qubits)
in which we explicitly separate the capacitive element from the Josephson
tunnel junction for improved qubit performance. The number of two-level systems
(TLS) that couple to the qubit is thereby reduced by an order of magnitude and
the measurement fidelity improves to 90%. This improved design enables the
first demonstration of quantum state tomography with superconducting qubits
using single shot measurements.Comment: submitted to PR
Microwave Dielectric Loss at Single Photon Energies and milliKelvin Temperatures
The microwave performance of amorphous dielectric materials at very low
temperatures and very low excitation strengths displays significant excess
loss. Here, we present the loss tangents of some common amorphous and
crystalline dielectrics, measured at low temperatures (T < 100 mK) with near
single-photon excitation energies, using both coplanar waveguide (CPW) and
lumped LC resonators. The loss can be understood using a two-level state (TLS)
defect model. A circuit analysis of the half-wavelength resonators we used is
outlined, and the energy dissipation of such a resonator on a multilayered
dielectric substrate is considered theoretically.Comment: 4 pages, 3 figures, submitted to Applied Physics Letter
Transformed Dissipation in Superconducting Quantum Circuits
Superconducting quantum circuits must be designed carefully to avoid
dissipation from coupling to external control circuitry. Here we introduce the
concept of current transformation to quantify coupling to the environment. We
test this theory with an experimentally-determined impedance transformation of
and find quantitative agreement better than a factor of 2 between
this transformation and the reduced lifetime of a phase qubit coupled to a
tunable transformer. Higher-order corrections from quantum fluctuations are
also calculated with this theory, but found not to limit the qubit lifetime. We
also illustrate how this simple connection between current and impedance
transformation can be used to rule out dissipation sources in experimental
qubit systems.Comment: 4 pages, 4 figure
Observation of bosonic coalescence of photon pairs
Quantum theory predicts that two indistinguishable photons incident on a
beam-splitter interferometer stick together as they exit the device (the pair
emerges randomly from one port or the other). We use a special
photon-number-resolving energy detector for a direct loophole-free observation
of this quantum-interference phenomenon. Simultaneous measurements from two
such detectors, one at each beam-splitter output port, confirm the absence of
cross-coincidences.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
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