445 research outputs found
Single spin detection by qubit SWAP to a molecular nanomagnet
Spin state detection is a key but very challenging step for any spin-based
solid-state quantum computing technology. In fullerene based quantum computer
technologies, we here propose to detect the single spin inside a fullerene by
transferring the quantum information from the endohedral spin to the ground
states of a molecular nanomagnet Fe, with large spin S=10. We show how to
perform the required SWAP operation and how to read out the information through
state-of-the-art techniques such as micro-SQUID.Comment: Europhysics Letters 69,699 (2005
Trapped-ion qutrit spin molecule quantum computer
We present a qutrit quantum computer design using trapped ions in the
presence of a magnetic field gradient. The magnetic field gradient induces a
"spin-spin" type coupling, similar to the J-coupling observed in molecules,
between the qutrits which allows conditional quantum logic to take place. We
describe in some detail, how one can execute specific one and two qutrit
quantum gates, required for universal qutrit quantum computing.Comment: 4 pages, 2 figure
A superconducting cavity bus for single Nitrogen Vacancy defect centres in diamond
Circuit-QED has demonstrated very strong coupling between individual
microwave photons trapped in a superconducting coplanar resonator and nearby
superconducting qubits. In this work we show how, by designing a novel
interconnect, one can strongly connect the superconducting resonator, via a
magnetic interaction, to a small number (perhaps single), of electronic spins.
By choosing the electronic spin to be within a Nitrogen Vacancy centre in
diamond one can perform optical readout, polarization and control of this
electron spin using microwave and radio frequency irradiation. More
importantly, by utilising Nitrogen Vacancy centres with nearby 13C nuclei,
using this interconnect, one has the potential build a quantum device where the
nuclear spin qubits are connected over centimeter distances via the Nitrogen
Vacancy electronic spins interacting through the superconducting bus.Comment: 4 pages, 6 figure
Adiabatic information transport in the presence of decoherence
We study adiabatic population transfer between discrete positions. Being
closely related to STIRAP in optical systems, this transport is coherent and
robust against variations of experimental parameters. Thanks to these
properties the scheme is a promising candidate for transport of quantum
information in quantum computing. We study the effects of spatially registered
noise sources on the quantum transport and in particular model Markovian
decoherence via non-local coupling to nearby quantum point contacts which serve
as information readouts. We find that the rate of decoherence experienced by a
spatial superposition initially grows with spatial separation but surprisingly
then plateaus. In addition we include non-Markovian effects due to couplings to
nearby two level systems and we find that although the population transport
exhibits robustness in the presence of both types of noise sources, the
transport of a spatial superposition exhibits severe fragility.Comment: 11page
Nanoscale magnetometry using a single spin system in diamond
We propose a protocol to estimate magnetic fields using a single
nitrogen-vacancy (N-V) center in diamond, where the estimate precision scales
inversely with time, ~1/T$, rather than the square-root of time. The method is
based on converting the task of magnetometry into phase estimation, performing
quantum phase estimation on a single N-V nuclear spin using either adaptive or
nonadaptive feedback control, and the recently demonstrated capability to
perform single-shot readout within the N-V [P. Neumann et. al., Science 329,
542 (2010)]. We present numerical simulations to show that our method provides
an estimate whose precision scales close to ~1/T (T is the total estimation
time), and moreover will give an unambiguous estimate of the static magnetic
field experienced by the N-V. By combining this protocol with recent proposals
for scanning magnetometry using an N-V, our protocol will provide a significant
decrease in signal acquisition time while providing an unambiguous spatial map
of the magnetic field.Comment: 8 pages and 5 figure
Readout scheme of the fullerene-based quantum computer by a single electron transistor
The readout of the quantum spin state is a challenge for any spin-based
quantum computing implementation. We propose a scheme, based on the achieved
technique of single electron transistor (SET), to implement the readout of
electronic spin state inside a doped fullerene by means of the
magnetic dipole-dipole coupling and spin filters. In the presence of an
external magnetic field, we show how to perform the spin state detection by
transforming the information contained in the spin state into the tunneling
current. The robustness of our scheme against sources of error is discussed.Comment: RevTex, 1 table and two figures. Latest versio
Superballistic Diffusion of Entanglement in Disordered Spin Chains
We study the dynamics of a single excitation in an infinite XXZ spin chain,
which is launched from the origin. We study the time evolution of the spread of
entanglement in the spin chain and obtain an expression for the second order
spatial moment of concurrence, about the origin, for both ordered and
disordered chains. In this way, we show that a finite central disordered region
can lead to sustained superballistic growth in the second order spatial moment
of entanglement within the chain.Comment: 5 pages, 1 figur
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