2,415 research outputs found
Accelerated Randomized Benchmarking
Quantum information processing offers promising advances for a wide range of
fields and applications, provided that we can efficiently assess the
performance of the control applied in candidate systems. That is, we must be
able to determine whether we have implemented a desired gate, and refine
accordingly. Randomized benchmarking reduces the difficulty of this task by
exploiting symmetries in quantum operations.
Here, we bound the resources required for benchmarking and show that, with
prior information, we can achieve several orders of magnitude better accuracy
than in traditional approaches to benchmarking. Moreover, by building on
state-of-the-art classical algorithms, we reach these accuracies with
near-optimal resources. Our approach requires an order of magnitude less data
to achieve the same accuracies and to provide online estimates of the errors in
the reported fidelities. We also show that our approach is useful for physical
devices by comparing to simulations.
Our results thus enable the application of randomized benchmarking in new
regimes, and dramatically reduce the experimental effort required to assess
control fidelities in quantum systems. Finally, our work is based on
open-source scientific libraries, and can readily be applied in systems of
interest.Comment: 10 pages, full source code at
https://github.com/cgranade/accelerated-randomized-benchmarking #quantuminfo
#benchmarkin
Spin diffusion of correlated two-spin states in a dielectric crystal
Reciprocal space measurements of spin diffusion in a single crystal of
calcium fluoride (CaF) have been extended to dipolar ordered states. The
experimental results for the component of the spin diffusion parallel with the
external field are cm/s for the
[001] direction and cm/s for the
[111] direction. The diffusion rates for dipolar order are significantly faster
than those for Zeeman order and are considerably faster than predicted by
simple theoretical models. It is suggested that constructive interference in
the transport of the two spin state is responsible for this enhancement. As
expected the anisotropy in the diffusion rates is observed to be significantly
less for dipolar order compared to the Zeeman case.Comment: 4 pages, 2 figures. Resubmitted to PRL - new figure added /
discussion expande
Simulations of Information Transport in Spin Chains
Transport of quantum information in linear spin chains has been the subject
of much theoretical work. Experimental studies by nuclear spin systems in
solid-state by NMR (a natural implementation of such models) is complicated
since the dipolar Hamiltonian is not solely comprised of nearest-neighbor
XY-Heisenberg couplings. We present here a similarity transformation between
the XY-Heisenberg Hamiltonian and the grade raising Hamiltonian, an interaction
which is achievable with the collective control provided by radio-frequency
pulses in NMR. Not only does this second Hamiltonian allows us to simulate the
information transport in a spin chain, but it also provides a means to observe
its signature experimentally
Extending Quantum Coherence in Diamond
We experimentally demonstrate over two orders of magnitude increase in the
coherence time of nitrogen vacancy centres in diamond by implementing
decoupling techniques. We show that equal pulse spacing decoupling performs
just as well as non-periodic Uhrig decoupling and has the additional benefit
that it allows us to take advantage of "revivals" in the echo (due to the
coherent nature of the bath) to explore the longest coherence times. At short
times, we can extend the coherence of particular quantum states out from
T_2*=2.7 us out to an effective T_2 > 340 us. For preserving arbitrary states
we show the experimental importance of using pulse sequences, that through
judicious choice of the phase of the pulses, compensate the imperfections of
individual pulses for all input states. At longer times we use these
compensated sequences to enhance the echo revivals and show a coherence time of
over 1.6 ms in ultra-pure natural abundance 13C diamond.Comment: 7 pages, 7 figures; minor syntax/typo. changes and updated reference
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