6,959 research outputs found
Vibrational transfer functions for base excited systems
Computer program GD203 develops transfer functions to compute governing vibration environment for complex structures subjected to a base motion
Efficient Refocussing of One Spin and Two Spin Interactions for NMR Quantum Computation
The use of spin echoes to refocus one spin interactions (chemical shifts) and
two spin interactions (spin-spin couplings) plays a central role in both
conventional NMR experiments and NMR quantum computation. Here we describe
schemes for efficient refocussing of such interactions in both fully and
partially coupled spin systems.Comment: 4 pages, RevTeX, including 4 LaTeX figure
Preparing pseudo-pure states with controlled-transfer gates
The preparation of pseudo-pure states plays a central role in the
implementation of quantum information processing in high temperature ensemble
systems, such as nuclear magnetic resonance. Here we describe a simple approach
based on controlled-transfer gates which permits pseudo-pure states to be
prepared efficiently using spatial averaging techniques.Comment: Significantly revised and extended: now 7 pages including 3 figures;
Phys. Rev. A (in press
Robust Logic Gates and Realistic Quantum Computation
The composite rotation approach has been used to develop a range of robust
quantum logic gates, including single qubit gates and two qubit gates, which
are resistant to systematic errors in their implementation. Single qubit gates
based on the BB1 family of composite rotations have been experimentally
demonstrated in a variety of systems, but little study has been made of their
application in extended computations, and there has been no experimental study
of the corresponding robust two qubit gates to date. Here we describe an
application of robust gates to Nuclear Magnetic Resonance (NMR) studies of
approximate quantum counting. We find that the BB1 family of robust gates is
indeed useful, but that the related NB1, PB1, B4 and P4 families of tailored
logic gates are less useful than initially expected.Comment: 6 pages RevTex4 including 5 figures (3 low quality to save space).
Revised at request of referee and incorporting minor corrections and updates.
Now in press at Phys Rev
NMR analogues of the quantum Zeno effect
We describe Nuclear Magnetic Resonance (NMR) demonstrations of the quantum
Zeno effect, and discuss briefly how these are related to similar phenomena in
more conventional NMR experiments.Comment: 8 pages including 4 figures; intended as a possible answer to Malcolm
Levitt's question at the 2005 Magnetic Resonanace GRC: "What is the NMR
analogue of the quantum Zeno effect?". In press at Physics Letters
Efficient decoupling schemes with bounded controls based on Eulerian orthogonal arrays
The task of decoupling, i.e., removing unwanted interactions in a system
Hamiltonian and/or couplings with an environment (decoherence), plays an
important role in controlling quantum systems. There are many efficient
decoupling schemes based on combinatorial concepts like orthogonal arrays,
difference schemes and Hadamard matrices. So far these (combinatorial)
decoupling schemes have relied on the ability to effect sequences of
instantaneous, arbitrarily strong control Hamiltonians (bang-bang controls). To
overcome the shortcomings of bang-bang control Viola and Knill proposed a
method called Eulerian decoupling that allows the use of bounded-strength
controls for decoupling. However, their method was not directly designed to
take advantage of the composite structure of multipartite quantum systems. In
this paper we define a combinatorial structure called an Eulerian orthogonal
array. It merges the desirable properties of orthogonal arrays and Eulerian
cycles in Cayley graphs (that are the basis of Eulerian decoupling). We show
that this structure gives rise to decoupling schemes with bounded-strength
control Hamiltonians that can be applied to composite quantum systems with few
body Hamiltonians and special couplings with the environment. Furthermore, we
show how to construct Eulerian orthogonal arrays having good parameters in
order to obtain efficient decoupling schemes.Comment: 8 pages, revte
Quantum Logic Gates and Nuclear Magnetic Resonance Pulse Sequences
We demonstrate how NMR can in principle be used to implement all the elements
required to build quantum computers, and briefly discuss the potential
applications of insights from quantum logic to the development of novel pulse
sequences with applications in more conventional NMR experiments.Comment: Sixteen pages, no figures. Submitted to Journal of Magnetic
Resonance. Primarily pedagogical rather than a description of novel research
result
Geometric quantum computation with NMR
The experimental realisation of the basic constituents of quantum information
processing devices, namely fault-tolerant quantum logic gates, requires
conditional quantum dynamics, in which one subsystem undergoes a coherent
evolution that depends on the quantum state of another subsystem. In
particular, the subsystem may acquire a conditional phase shift. Here we
consider a novel scenario in which this phase is of geometric rather than
dynamical origin. As the conditional geometric (Berry) phase depends only on
the geometry of the path executed it is resilient to certain types of errors,
and offers the potential of an intrinsically fault-tolerant way of performing
quantum gates. Nuclear Magnetic Resonance (NMR) has already been used to
demonstrate both simple quantum information processing and Berry's phase. Here
we report an NMR experiment which implements a conditional Berry phase, and
thus a controlled phase shift gate. This constitutes the first elementary
geometric quantum computation.Comment: Minor additions at request of referees. 4 pages revtex including 2
figures (1 eps). Nature in pres
Compiling gate networks on an Ising quantum computer
Here we describe a simple mechanical procedure for compiling a quantum gate
network into the natural gates (pulses and delays) for an Ising quantum
computer. The aim is not necessarily to generate the most efficient pulse
sequence, but rather to develop an efficient compilation algorithm that can be
easily implemented in large spin systems. The key observation is that it is not
always necessary to refocus all the undesired couplings in a spin system.
Instead the coupling evolution can simply be tracked and then corrected at some
later time. Although described within the language of NMR the algorithm is
applicable to any design of quantum computer based on Ising couplings.Comment: 5 pages RevTeX4 including 4 figures. Will submit to PR
Implementation of Conditional Phase Shift gate for Quantum Information Processing by NMR, using Transition-selective pulses
Experimental realization of quantum information processing in the field of
nuclear magnetic resonance (NMR) has been well established. Implementation of
conditional phase shift gate has been a significant step, which has lead to
realization of important algorithms such as Grover's search algorithm and
quantum Fourier transform. This gate has so far been implemented in NMR by
using coupling evolution method. We demonstrate here the implementation of the
conditional phase shift gate using transition selective pulses. As an
application of the gate, we demonstrate Grover's search algorithm and quantum
Fourier transform by simulations and experiments using transition selective
pulses.Comment: 14 pages, 5 figure
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