339 research outputs found
Circuit QED and engineering charge based superconducting qubits
The last two decades have seen tremendous advances in our ability to generate
and manipulate quantum coherence in mesoscopic superconducting circuits. These
advances have opened up the study of quantum optics of microwave photons in
superconducting circuits as well as providing important hardware for the
manipulation of quantum information. Focusing primarily on charge-based qubits,
we provide a brief overview of these developments and discuss the present state
of the art. We also survey the remarkable progress that has been made in
realizing circuit quantum electrodynamics (QED) in which superconducting
artificial atoms are strongly coupled to individual microwave photons.Comment: Proceedings of Nobel Symposium 141: Qubits for Future Quantum
Informatio
The millimeter-wave properties of superconducting microstrip lines
We have developed a novel technique for making high quality measurements of the millimeter-wave properties of superconducting thin-film microstrip transmission lines. Our experimental technique currently covers the 75-100 GHz band. The method is based on standing wave resonances in an open ended transmission line. We obtain information on the phase velocity and loss of the microstrip. Our data for Nb/SiO/Nb lines, taken at 4.2 K and 1.6 K, can be explained by a single set of physical parameters. Our preliminary conclusion is that the loss is dominated by the SiO dielectric, with a temperature-independent loss tangent of 5.3 ± 0.5 x 10^(-3) for our samples
Introduction to Quantum Noise, Measurement and Amplification
The topic of quantum noise has become extremely timely due to the rise of
quantum information physics and the resulting interchange of ideas between the
condensed matter and AMO/quantum optics communities. This review gives a
pedagogical introduction to the physics of quantum noise and its connections to
quantum measurement and quantum amplification. After introducing quantum noise
spectra and methods for their detection, we describe the basics of weak
continuous measurements. Particular attention is given to treating the standard
quantum limit on linear amplifiers and position detectors using a general
linear-response framework. We show how this approach relates to the standard
Haus-Caves quantum limit for a bosonic amplifier known in quantum optics, and
illustrate its application for the case of electrical circuits, including
mesoscopic detectors and resonant cavity detectors.Comment: Substantial improvements over initial version; include supplemental
appendices
Hardware-efficient autonomous quantum error correction
We propose a new method to autonomously correct for errors of a logical qubit
induced by energy relaxation. This scheme encodes the logical qubit as a
multi-component superposition of coherent states in a harmonic oscillator, more
specifically a cavity mode. The sequences of encoding, decoding and correction
operations employ the non-linearity provided by a single physical qubit coupled
to the cavity. We layout in detail how to implement these operations in a
practical system. This proposal directly addresses the task of building a
hardware-efficient and technically realizable quantum memory.Comment: 12 pages,6 figure
Deterministic protocol for mapping a qubit to coherent state superpositions in a cavity
We introduce a new gate that transfers an arbitrary state of a qubit into a
superposition of two quasi-orthogonal coherent states of a cavity mode, with
opposite phases. This qcMAP gate is based on conditional qubit and cavity
operations exploiting the energy level dispersive shifts, in the regime where
they are much stronger than the cavity and qubit linewidths. The generation of
multi-component superpositions of quasi-orthogonal coherent states, non-local
entangled states of two resonators and multi-qubit GHZ states can be
efficiently achieved by this gate
Dynamically protected cat-qubits: a new paradigm for universal quantum computation
We present a new hardware-efficient paradigm for universal quantum
computation which is based on encoding, protecting and manipulating quantum
information in a quantum harmonic oscillator. This proposal exploits
multi-photon driven dissipative processes to encode quantum information in
logical bases composed of Schr\"odinger cat states. More precisely, we consider
two schemes. In a first scheme, a two-photon driven dissipative process is used
to stabilize a logical qubit basis of two-component Schr\"odinger cat states.
While such a scheme ensures a protection of the logical qubit against the
photon dephasing errors, the prominent error channel of single-photon loss
induces bit-flip type errors that cannot be corrected. Therefore, we consider a
second scheme based on a four-photon driven dissipative process which leads to
the choice of four-component Schr\"odinger cat states as the logical qubit.
Such a logical qubit can be protected against single-photon loss by continuous
photon number parity measurements. Next, applying some specific Hamiltonians,
we provide a set of universal quantum gates on the encoded qubits of each of
the two schemes. In particular, we illustrate how these operations can be
rendered fault-tolerant with respect to various decoherence channels of
participating quantum systems. Finally, we also propose experimental schemes
based on quantum superconducting circuits and inspired by methods used in
Josephson parametric amplification, which should allow to achieve these driven
dissipative processes along with the Hamiltonians ensuring the universal
operations in an efficient manner.Comment: 28 pages, 11 figure
Tunable dynamical channel blockade in double-dot Aharonov-Bohm interferometers
We study electronic transport through an Aharonov-Bohm interferometer with
single-level quantum dots embedded in the two arms. The full counting
statistics in the shot-noise regime is calculated to first order in the
tunnel-coupling strength. The interplay of interference and charging energy in
the dots leads to a dynamical channel blockade that is tunable by the magnetic
flux penetrating the Aharonov-Bohm ring. We find super-Poissonian behavior with
diverging second and higher cumulants when the Aharonov-Bohm flux approaches an
integer multiple of the flux quantum.Comment: published version, 10 pages, 10 figure
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