1,250 research outputs found
Efficient one- and two-qubit pulsed gates for an oscillator stabilized Josephson qubit
We present theoretical schemes for performing high-fidelity one- and
two-qubit pulsed gates for a superconducting flux qubit. The "IBM qubit"
consists of three Josephson junctions, three loops, and a superconducting
transmission line. Assuming a fixed inductive qubit-qubit coupling, we show
that the effective qubit-qubit interaction is tunable by changing the applied
fluxes, and can be made negligible, allowing one to perform high fidelity
single qubit gates. Our schemes are tailored to alleviate errors due to 1/f
noise; we find gates with only 1% loss of fidelity due to this source, for
pulse times in the range of 20-30ns for one-qubit gates (Z rotations,
Hadamard), and 60ns for a two-qubit gate (controlled-Z). Our relaxation and
dephasing time estimates indicate a comparable loss of fidelity from this
source. The control of leakage plays an important role in the design of our
shaped pulses, preventing shorter pulse times. However, we have found that
imprecision in the control of the quantum phase plays the major role in the
limitation of the fidelity of our gates.Comment: Published version. Added references. Corrected minor typos. Added
discussion on how the influence of 1/f noise is modeled. 36 pages, 11 figure
Encoding a Qubit into a Cavity Mode in Circuit-QED using Phase Estimation
Gottesman, Kitaev and Preskill have formulated a way of encoding a qubit into
an oscillator such that the qubit is protected against small shifts
(translations) in phase space. The idea underlying this encoding is that error
processes of low rate can be expanded into small shift errors. The qubit space
is defined as an eigenspace of two mutually commuting displacement operators
and which act as large shifts/translations in phase space. We
propose and analyze the approximate creation of these qubit states by coupling
the oscillator to a sequence of ancilla qubits. This preparation of the states
uses the idea of phase estimation where the phase of the displacement operator,
say , is approximately determined. We consider several possible forms of
phase estimation. We analyze the performance of repeated and adapative phase
estimation as the simplest and experimentally most viable schemes given a
realistic upper-limit on the number of photons in the oscillator. We propose a
detailed physical implementation of this protocol using the dispersive coupling
between a transmon ancilla qubit and a cavity mode in circuit-QED. We provide
an estimate that in a current experimental set-up one can prepare a good code
state from a squeezed vacuum state using rounds of adapative phase
estimation, lasting in total about sec., with (heralded) chance
of success.Comment: 24 pages, 15 figures. Some minor improvements to text and figures.
Some of the numerical data has been replaced by more accurate simulations.
The improved simulation shows that the code performs better than originally
anticipate
Superconducting Quantum Circuits, Qubits and Computing
This paper gives an introduction to the physics and principles of operation
of quantized superconducting electrical circuits for quantum information
processing.Comment: 59 pages 68 figures. Prepared for Handbook of Theoretical and
Computational Nanotechnolog
Quantum Logic for Trapped Atoms via Molecular Hyperfine Interactions
We study the deterministic entanglement of a pair of neutral atoms trapped in
an optical lattice by coupling to excited-state molecular hyperfine potentials.
Information can be encoded in the ground-state hyperfine levels and processed
by bringing atoms together pair-wise to perform quantum logical operations
through induced electric dipole-dipole interactions. The possibility of
executing both diagonal and exchange type entangling gates is demonstrated for
two three-level atoms and a figure of merit is derived for the fidelity of
entanglement. The fidelity for executing a CPHASE gate is calculated for two
87Rb atoms, including hyperfine structure and finite atomic localization. The
main source of decoherence is spontaneous emission, which can be minimized for
interaction times fast compared to the scattering rate and for sufficiently
separated atomic wavepackets. Additionally, coherent couplings to states
outside the logical basis can be constrained by the state dependent trapping
potential.Comment: Submitted to Physical Review
Quantum Algorithms for Fermionic Simulations
We investigate the simulation of fermionic systems on a quantum computer. We
show in detail how quantum computers avoid the dynamical sign problem present
in classical simulations of these systems, therefore reducing a problem
believed to be of exponential complexity into one of polynomial complexity. The
key to our demonstration is the spin-particle connection (or generalized
Jordan-Wigner transformation) that allows exact algebraic invertible mappings
of operators with different statistical properties. We give an explicit
implementation of a simple problem using a quantum computer based on standard
qubits.Comment: 38 pages, 2 psfigur
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Comparison of time-domain and frequency-domain phase noise analyses
This thesis presents a comparison of time-domain and frequency-domain algorithms for phase noise calculation in oscillators. Floquet theory provides the mathematical foundation for these calculations and the numerical methods employ perturbation projection vectors (PPVs). The PPVs are an estimate of an oscillator's sensitivity to noise.
The in-house circuit simulator SPICE3 has been extended to phase noise analysis based on both the time-domain and frequency-domain periodic steadystate analyses. These analysis methods have been evaluated on a wide suite of test oscillators. A detailed comparison of these methods is carried out in terms of
accuracy and computation costs. The SPICE3 version with PPV calculation and phase noise analysis is a powerful tool for design of noise tolerant oscillators.Keywords: phase noise, oscillator
A Circuit Theory Perspective on the Modeling and Analysis of Vibration Energy Harvesting Systems: A Review
This paper reviews advanced modeling and analysis techniques useful in the description, design, and optimization of mechanical energy harvesting systems based on the collection of energy from vibration sources. The added value of the present contribution is to demonstrate the benefits of the exploitation of advanced techniques, most often inherited from other fields of physics and engineering, to improve the performance of such systems. The review is focused on the modeling techniques that apply to the entire energy source/mechanical oscillator/transducer/electrical load chain, describing mechanical–electrical analogies to represent the collective behavior as the cascade of equivalent electrical two-ports, introducing matching networks enhancing the energy transfer to the load, and discussing the main numerical techniques in the frequency and time domains that can be used to analyze linear and nonlinear harvesters, both in the case of deterministic and stochastic excitations
Characterization and Design of Analog Integrated Circuits Exploiting Analog Platforms
Universal Mobile Telecommunication System (UMTS) front end design is challenging because of the need to optimize power while satisfying a very high dynamic range requirement. At the same time, designing analog circuits for automotive applications is very difficult because of the wide temperature range (from -40 to 125 degrees at least) they must tolerate. Dealing with this design problems at the transistor level does not allow to explore efficiently the design space, while using behavioral models does not allow to take into consideration important second-order effects. We present an extension of the platform-based design methodology originally developed for digital systems to the analog domain to conjugate the need of higher levels of abstraction to deal with complexity as well as the one of capturing enough of the actual circuit-level characteristics to deal with second order effects. This methodology is based on the concept of Analog Platform and is very useful both to characterize an analog circuit and to perform a system level optimization. We show how this methodology applied to the UMTS front-end design yields power savings as large as 47% versus an original hand optimized design. Besides, we give details on how to design an RC oscillator for automotive applications and to get its main performances at the aim of characterizing it
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