406 research outputs found
Anisotropic Stark Effect and Electric-Field Noise Suppression for Phosphorus Donor Qubits in Silicon
We report the use of novel, capacitively terminated coplanar waveguide (CPW)
resonators to measure the quadratic Stark shift of phosphorus donor qubits in
Si. We confirm that valley repopulation leads to an anisotropic spin-orbit
Stark shift depending on electric and magnetic field orientations relative to
the Si crystal. By measuring the linear Stark effect, we estimate the effective
electric field due to strain in our samples. We show that in the presence of
this strain, electric-field sources of decoherence can be non-negligible. Using
our measured values for the Stark shift, we predict magnetic fields for which
the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing
decoherence from electric-field noise. We discuss the limitations of these
noise-suppression points due to random distributions of strain and propose a
method for overcoming them
Addressing spin transitions on 209Bi donors in silicon using circularly-polarized microwaves
Over the past decade donor spin qubits in isotopically enriched Si
have been intensely studied due to their exceptionally long coherence times.
More recently bismuth donor electron spins have become popular because Bi has a
large nuclear spin which gives rise to clock transitions (first-order
insensitive to magnetic field noise). At every clock transition there are two
nearly degenerate transitions between four distinct states which can be used as
a pair of qubits. Here it is experimentally demonstrated that these transitions
are excited by microwaves of opposite helicity such that they can be
selectively driven by varying microwave polarization. This work uses a
combination of a superconducting coplanar waveguide (CPW) microresonator and a
dielectric resonator to flexibly generate arbitrary elliptical polarizations
while retaining the high sensitivity of the CPW
Spin relaxation and coherence times for electrons at the Si/SiO2 interface
While electron spins in silicon heterostructures make attractive qubits,
little is known about the coherence of electrons at the Si/SiO2 interface. We
report spin relaxation (T1) and coherence (T2) times for mobile electrons and
natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1
and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and
cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is
around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by
a factor of two. The quantum dot T2 is shorter than T1, indicating that T2 is
not controlled by T1 at 350 mK but is instead limited by an extrinsic
mechanism. The evidence suggests that this extrinsic mechanism is an exchange
interaction between electrons in neighboring dots.Comment: Extended with more experiments and rewritten. 6 pages, 5 figures, to
be submitted to Phys. Rev.
Nitrogen and Phosphorus Salts Treatment Effect to Spot Blotch Development on Barley
The paper presents the data on seedling and adult resistance to dark-brown leaf spot blotch (Bipolaris sorokiniana) in barley samples described in modern literature as resistant to the disease and in varieties allowed growing in the territory of Russian Federation. All 32 samples and 69 varieties under study were highly susceptible to the blotch at both growth stages. This fact indicates to urgent need in developing new methodes for dark-brown leaf spot blotch protection. Treatment of barley plants varieties with mixture of nitrogen and phosphorus salts solution reduced the disease development on seedlings of 13 commercial varieties and on adult plants of 36 varieties (52 % out of all studied). For all these 36 varieties weight of 1000 grains was significantly higher on treated plots compared to untreated ones for 11–108 %. The mechanism of nitrogen and phosphorus salts effect on the dark-brown leaf spot blotch development (changing virulence/aggressiveness of the pathogen) indicates that change of the salts concentrations and their ratio in the solution could expand the set of host plants genotypes on which this treatment will decrease the disease development
Spin Coherence and N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR
Pulsed ESR experiments are reported for ensembles of negatively-charged
nitrogen-vacancy centers (NV) in diamonds at X-band magnetic fields
(280-400 mT) and low temperatures (2-70 K). The NV centers in synthetic
type IIb diamonds (nitrogen impurity concentration ~ppm) are prepared with
bulk concentrations of cm to cm
by high-energy electron irradiation and subsequent annealing. We find that a
proper post-radiation anneal (1000C for 60 mins) is critically
important to repair the radiation damage and to recover long electron spin
coherence times for NVs. After the annealing, spin coherence times of T~ms at 5~K are achieved, being only limited by C nuclear spectral
diffusion in natural abundance diamonds. At X-band magnetic fields, strong
electron spin echo envelope modulation (ESEEM) is observed originating from the
central N nucleus. The ESEEM spectral analysis allows for accurate
determination of the N nuclear hypefine and quadrupole tensors. In
addition, the ESEEM effects from two proximal C sites (second-nearest
neighbor and fourth-nearest neighbor) are resolved and the respective C
hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure
Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy
We discuss the design and implementation of thin film superconducting
coplanar waveguide micro- resonators for pulsed ESR experiments. The
performance of the resonators with P doped Si epilayer samples is compared to
waveguide resonators under equivalent conditions. The high achievable filling
factor even for small sized samples and the relatively high Q-factor result in
a sensitivity that is superior to that of conventional waveguide resonators, in
particular to spins close to the sample surface. The peak microwave power is on
the order of a few microwatts, which is compatible with measurements at ultra
low temperatures. We also discuss the effect of the nonuniform microwave
magnetic field on the Hahn echo power dependence
Mathematical investigation of tsunami-like long waves interaction with submerge dike of different thickness
This paper presents a mathematical investigation of the interaction of a long tsunami-type wave with a submerge dike. The calculations were performed by using the freeware package OpenFOAM. Unsteady two-dimensional Navier-Stokes equations were used for mathematical modeling of incompressible two-phase medium. The Volume of Fluid (VOF) method is used to capture the free surface of a liquid. The effects caused by long wave of defined amplitude motion through a submerged dike of varying thickness were discussed in detail. Numerical results show that after wave passing through the barrier, multiple vortex structures were formed behind. Intensity of vortex depended on the size of the barrier. The effectiveness of the submerge barrier was estimated by evaluating the wave reflection and transmission coefficients using the energy integral method. Then, the curves of the dependences of the reflection and transmission coefficients were obtained for the interaction of waves with the dike. Finally, it was confirmed that the energy of the wave could be reduced by more than 50% when it passed through the barrier
Will spin-relaxation times in molecular magnets permit quantum information processing?
Using X-band pulsed electron spin resonance, we report the intrinsic
spin-lattice () and phase coherence () relaxation times in molecular
nanomagnets for the first time. In Cr heterometallic wheels, with = Ni
and Mn, phase coherence relaxation is dominated by the coupling of the electron
spin to protons within the molecule. In deuterated samples reaches 3
s at low temperatures, which is several orders of magnitude longer than
the duration of spin manipulations, satisfying a prerequisite for the
deployment of molecular nanomagnets in quantum information applications.Comment: 4 pages, 3 figures, in press at Physical Review Letter
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