23,183 research outputs found
Switchable coupling for superconducting qubits using double resonance in the presence of crosstalk
Several methods have been proposed recently to achieve switchable coupling
between superconducting qubits. We discuss some of the main considerations
regarding the feasibility of implementing one of those proposals: the
double-resonance method. We analyze mainly issues related to the achievable
effective coupling strength and the effects of crosstalk on this coupling
approach. We also find a new, crosstalk-assisted coupling channel that can be
an attractive alternative when implementing the double-resonance coupling
proposal.Comment: 4 pages, 3 figure
On the heating of source of the Orion KL hot core
We present images of the J=10-9 rotational lines of HC3N in the vibrationally
excited levels 1v7, 1v6 and 1v5 of the hot core (HC) in Orion KL. The images
show that the spatial distribution and the size emission from the 1v7 and 1v5
levels are different. While the J=10-9 1v7 line has a size of 4''x 6'' and
peaks 1.1'' NE of the 3 mm continuum peak, the J=10--9 1v5 line emission is
unresolved (<3'') and peaks 1.3'' south of the 3 mm peak. This is a clear
indication that the HC is composed of condensations with very different
temperatures (170 K for the 1v7 peak and K for the 1v5 peak). The
temperature derived from the 1v7 and 1v5 lines increases with the projected
distance to the suspected main heating source I. Projection effects along the
line of sight could explain the temperature gradient as produced by source I.
However, the large luminosity required for source I, >5 10^5 Lsolar, to explain
the 1v5 line suggests that external heating by this source may not dominate the
heating of the HC. Simple model calculations of the vibrationally excited
emission indicate that the HC can be internally heated by a source with a
luminosity of 10^5 Lsolar, located 1.2'' SW of the 1v5 line peak (1.8'' south
of source I). We also report the first detection of high-velocity gas from
vibrationally excited HC3N emission. Based on excitation arguments we conclude
that the main heating source is also driving the molecular outflow. We
speculate that all the data presented in this letter and the IR images are
consistent with a young massive protostar embedded in an edge-on disk.Comment: 13 pages, 3 figures, To be published in Ap.J. Letter
Speed limits for quantum gates in multi-qubit systems
We use analytical and numerical calculations to obtain speed limits for
various unitary quantum operations in multiqubit systems under typical
experimental conditions. The operations that we consider include single-, two-,
and three-qubit gates, as well as quantum-state transfer in a chain of qubits.
We find in particular that simple methods for implementing two-qubit gates
generally provide the fastest possible implementations of these gates. We also
find that the three-qubit Toffoli gate time varies greatly depending on the
type of interactions and the system's geometry, taking only slightly longer
than a two-qubit controlled-NOT (CNOT) gate for a triangle geometry. The speed
limit for quantum-state transfer across a qubit chain is set by the maximum
spin-wave speed in the chain.Comment: 7 pages (two-column), 2 figures, 2 table
Quantum state transfer via temporal kicking of information
We propose a strategy for perfect state transfer in spin chains based on the
use of an unmodulated coupling Hamiltonian whose coefficients are explicitly
time dependent. We show that, if specific and non-demanding conditions are
satisfied by the temporal behavior of the coupling strengths, our model allows
perfect state transfer. The paradigma put forward by our proposal holds the
promises to set an alternative standard to the use of clever encoding and
coupling-strength engineering for perfect state transfer.Comment: 7 pages, 7 figures, RevTeX
A Web-Based Distributed Virtual Educational Laboratory
Evolution and cost of measurement equipment, continuous training, and distance learning make it difficult to provide a complete set of updated workbenches to every student. For a preliminary familiarization and experimentation with instrumentation and measurement procedures, the use of virtual equipment is often considered more than sufficient from the didactic point of view, while the hands-on approach with real instrumentation and measurement systems still remains necessary to complete and refine the student's practical expertise. Creation and distribution of workbenches in networked computer laboratories therefore becomes attractive and convenient. This paper describes specification and design of a geographically distributed system based on commercially standard components
Criterios de robustez para sistemas lineales
Al construir un modelo de un sistema, éste siempre incluye algún grado de incertidumbre con respecto al sistema real y a su entorno. El sistema puede cambiar de manera inesperada o estar sujeto a perturbaciones inesperadas. Debido a factores como los cambios en los parámetros, las dinámicas y retardos no modeladas, los cambios en los puntos de operación, el ruido en los sensores o las perturbaciones no predichas, el modelo de un proceso no puede ser una representación completamente acertada del sistema real [1]
Selective darkening of degenerate transitions for implementing quantum controlled-NOT gates
We present a theoretical analysis of the selective darkening method for
implementing quantum controlled-NOT (CNOT) gates. This method, which we
recently proposed and demonstrated, consists of driving two
transversely-coupled quantum bits (qubits) with a driving field that is
resonant with one of the two qubits. For specific relative amplitudes and
phases of the driving field felt by the two qubits, one of the two transitions
in the degenerate pair is darkened, or in other words, becomes forbidden by
effective selection rules. At these driving conditions, the evolution of the
two-qubit state realizes a CNOT gate. The gate speed is found to be limited
only by the coupling energy J, which is the fundamental speed limit for any
entangling gate. Numerical simulations show that at gate speeds corresponding
to 0.48J and 0.07J, the gate fidelity is 99% and 99.99%, respectively, and
increases further for lower gate speeds. In addition, the effect of
higher-lying energy levels and weak anharmonicity is studied, as well as the
scalability of the method to systems of multiple qubits. We conclude that in
all these respects this method is competitive with existing schemes for
creating entanglement, with the added advantages of being applicable for qubits
operating at fixed frequencies (either by design or for exploitation of
coherence sweet-spots) and having the simplicity of microwave-only operation.Comment: 25 pages, 5 figure
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