8,985 research outputs found
Spin characterization and control over the regime of radiation-induced zero-resistance states
Over the regime of the radiation-induced zero-resistance states and
associated oscillatory magnetoresistance, we propose a low magnetic field
analog of quantum-Hall-limit techniques for the electrical detection of
electron spin- and nuclear magnetic- resonance, dynamical nuclear polarization
via electron spin resonance, and electrical characterization of the nuclear
spin polarization via the Overhauser shift. In addition, beats observed in the
radiation-induced oscillatory-magnetoresistance are developed into a method to
measure and control the zero-field spin splitting due to the Bychkov-Rashba and
bulk inversion asymmetry terms in the high mobility GaAs/AlGaAs system.Comment: IEEE Transactions in Nanotechnology (to be published); 10 pages, 10
color figure
Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond
We map out the first excited state sublevel structure of single nitrogen-vacancy (NV) colour centres in diamond. The excited state is an orbital doublet where one branch supports an efficient cycling transition, while the other can simultaneously support fully allowed optical Raman spin-flip transitions. This is crucial for the success of many recently proposed quantum information applications of the NV defects. We further find that an external electric field can be used to completely control the optical properties of a single centre. Finally, a group theoretical model is developed that explains the observations and provides good physical understanding of the excited state structure
Applications of quantum cryptographic switch: Various tasks related to controlled quantum communication can be performed using Bell states and permutation of particles
Recently, several aspects of controlled quantum communication (e.g.,
bidirectional controlled state teleportation, controlled quantum secure direct
communication, controlled quantum dialogue, etc.) have been studied using
-qubit () entanglement. Specially, a large number of schemes for
bidirectional controlled state teleportation are proposed using -qubit
entanglement (). Here, we propose a set of protocols to
illustrate that it is possible to realize all these tasks related to controlled
quantum communication using only Bell states and permutation of particles
(PoP). As the generation and maintenance of a Bell state is much easier than a
multi-partite entanglement, the proposed strategy has a clear advantage over
the existing proposals. Further, it is shown that all the schemes proposed here
may be viewed as applications of the concept of quantum cryptographic switch
which was recently introduced by some of us. The performances of the proposed
protocols as subjected to the amplitude damping and phase damping noise on the
channels are also discussed.Comment: 12 pages, 3 figure
On the group theoretic structure of a class of quantum dialogue protocols
Intrinsic symmetry of the existing protocols of quantum dialogue are
explored. It is shown that if we have a set of mutually orthogonal -qubit
states {\normalsize
and a set of
() unitary operators
and
forms a group under multiplication then it
would be sufficient to construct a quantum dialogue protocol using this set of
quantum states and this group of unitary operators}. The sufficiency condition
is used to provide a generalized protocol of quantum dialogue. Further the
basic concepts of group theory and quantum mechanics are used here to
systematically generate several examples of possible groups of unitary
operators that may be used for implementation of quantum dialogue. A large
number of examples of quantum states that may be used to implement the
generalized quantum dialogue protocol using these groups of unitary operators
are also obtained. For example, it is shown that GHZ state, GHZ-like state, W
state, 4 and 5 qubit Cluster states, Omega state, Brown state, state
and state can be used for implementation of quantum dialogue protocol.
The security and efficiency of the proposed protocol is appropriately analyzed.
It is also shown that if a group of unitary operators and a set of mutually
orthogonal states are found to be suitable for quantum dialogue then they can
be used to provide solutions of socialist millionaire problem.Comment: 15 page
Polytype control of spin qubits in silicon carbide
Crystal defects can confine isolated electronic spins and are promising
candidates for solid-state quantum information. Alongside research focusing on
nitrogen vacancy centers in diamond, an alternative strategy seeks to identify
new spin systems with an expanded set of technological capabilities, a
materials driven approach that could ultimately lead to "designer" spins with
tailored properties. Here, we show that the 4H, 6H and 3C polytypes of SiC all
host coherent and optically addressable defect spin states, including spins in
all three with room-temperature quantum coherence. The prevalence of this spin
coherence shows that crystal polymorphism can be a degree of freedom for
engineering spin qubits. Long spin coherence times allow us to use double
electron-electron resonance to measure magnetic dipole interactions between
spin ensembles in inequivalent lattice sites of the same crystal. Together with
the distinct optical and spin transition energies of such inequivalent spins,
these interactions provide a route to dipole-coupled networks of separately
addressable spins.Comment: 28 pages, 5 figures, and supplementary information and figure
Identification and tunable optical coherent control of transition-metal spins in silicon carbide
Color centers in wide-bandgap semiconductors are attractive systems for
quantum technologies since they can combine long-coherent electronic spin and
bright optical properties. Several suitable centers have been identified, most
famously the nitrogen-vacancy defect in diamond. However, integration in
communication technology is hindered by the fact that their optical transitions
lie outside telecom wavelength bands. Several transition-metal impurities in
silicon carbide do emit at and near telecom wavelengths, but knowledge about
their spin and optical properties is incomplete. We present all-optical
identification and coherent control of molybdenum-impurity spins in silicon
carbide with transitions at near-infrared wavelengths. Our results identify
spin for both the electronic ground and excited state, with highly
anisotropic spin properties that we apply for implementing optical control of
ground-state spin coherence. Our results show optical lifetimes of 60 ns
and inhomogeneous spin dephasing times of 0.3 s, establishing
relevance for quantum spin-photon interfacing.Comment: Updated version with minor correction, full Supplementary Information
include
Designing defect-based qubit candidates in wide-gap binary semiconductors for solid-state quantum technologies
The development of novel quantum bits is key to extend the scope of
solid-state quantum information science and technology. Using first-principles
calculations, we propose that large metal ion - vacancy complexes are promising
qubit candidates in two binary crystals: 4H-SiC and w-AlN. In particular, we
found that the formation of neutral Hf- and Zr-vacancy complexes is
energetically favorable in both solids; these defects have spin-triplet ground
states, with electronic structures similar to those of the diamond NV center
and the SiC di-vacancy. Interestingly, they exhibit different spin-strain
coupling characteristics, and the nature of heavy metal ions may allow for easy
defect implantation in desired lattice locations and ensure stability against
defect diffusion. In order to support future experimental identification of the
proposed defects, we report predictions of their optical zero-phonon line,
zero-field splitting and hyperfine parameters. The defect design concept
identified here may be generalized to other binary semiconductors to facilitate
the exploration of new solid-state qubits.Comment: 23 pages, 5 figures, 6 tables, Supplementary Information is added at
the en
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