236 research outputs found
Memory cell based on a Josephson junction
The Josephson junction has a doubly degenerate ground state with
the Josephson phases . We demonstrate the use of such a
Josephson junction as a memory cell (classical bit), where writing is done by
applying a magnetic field and reading by applying a bias current. In the
"store" state, the junction does not require any bias or magnetic field, but
just needs to stay cooled for permanent storage of the logical bit.
Straightforward integration with Rapid Single Flux Quantum logic is possible.Comment: to be published in AP
Phase retrapping in aφJosephson junction: onset of the butterfly effect
We investigate experimentally the retrapping of the phase in a
φ
Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile
U
0
(
ψ
)
in
φ
JJ is a
2
Ï€
periodic double-well potential with minima at
ψ
=
±
φ
mod
2
Ï€
, the question is at which of the two minima
−
φ
or
+
φ
the phase will be trapped upon return from a finite voltage state during quasistatic decrease of the bias current (tilt of the potential). By measuring the relative population of two peaks in escape histograms, we determine the probability of phase trapping in the
±
φ
wells for different temperatures. Our experimental results agree qualitatively with theoretical predictions. In particular, we observe an onset of the butterfly effect with an oscillating probability of trapping. Unexpectedly, this probability saturates at a value different from 50% at low temperatures
Spectroscopy of a fractional Josephson vortex molecule
In long Josephson junctions with multiple discontinuities of the Josephson
phase, fractional vortex molecules are spontaneously formed. At each
discontinuity point a fractional Josephson vortex carrying a magnetic flux
, Wb being the magnetic flux
quantum, is pinned. Each vortex has an oscillatory eigenmode with a frequency
that depends on and lies inside the plasma gap.
We experimentally investigate the dependence of the eigenfrequencies of a
two-vortex molecule on the distance between the vortices, on their topological
charge and on the bias current applied to the
Josephson junction. We find that with decreasing distance between vortices, a
splitting of the eigenfrequencies occurs, that corresponds to the emergence of
collective oscillatory modes of both vortices. We use a resonant microwave
spectroscopy technique and find good agreement between experimental results and
theoretical predictions.Comment: submitted to Phys. Rev.
Experimental evidence of a {\phi} Josephson junction
We demonstrate experimentally the existence of Josephson junctions having a
doubly degenerate ground state with an average Josephson phase \psi=\pm{\phi}.
The value of {\phi} can be chosen by design in the interval 0<{\phi}<\pi. The
junctions used in our experiments are fabricated as 0-{\pi} Josephson junctions
of moderate normalized length with asymmetric 0 and {\pi} regions. We show that
(a) these {\phi} Josephson junctions have two critical currents, corresponding
to the escape of the phase {\psi} from -{\phi} and +{\phi} states; (b) the
phase {\psi} can be set to a particular state by tuning an external magnetic
field or (c) by using a proper bias current sweep sequence. The experimental
observations are in agreement with previous theoretical predictions
Probing the Y2 Receptor on Transmembrane, Intra- and Extra-Cellular Sites for EPR Measurements
The function of G protein-coupled receptors is intrinsically linked to their conformational dynamics. In conjugation with site-directed spin labeling, electron paramagnetic resonance (EPR) spectroscopy provides powerful tools to study the highly dynamic conformational states of these proteins. Here, we explored positions for nitroxide spin labeling coupled to single cysteines, introduced at transmembrane, intra- and extra-cellular sites of the human neuropeptide Y2 receptor. Receptor mutants were functionally analyzed in cell culture system, expressed in Escherichia coli fermentation with yields of up to 10 mg of purified protein per liter expression medium and functionally reconstituted into a lipid bicelle environment. Successful spin labeling was confirmed by a fluorescence assay and continuous wave EPR measurements. EPR spectra revealed mobile and immobile populations, indicating multiple dynamic conformational states of the receptor. We found that the singly mutated positions by MTSL ((1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl) methyl methanesulfonothioate) have a water exposed immobilized conformation as their main conformation, while in case of the IDSL (bis(1-oxyl-2,2,5,5-tetramethyl-3-imidazolin-4-yl) disulfide) labeled positions, the main conformation are mainly of hydrophobic nature. Further, double cysteine mutants were generated and examined for potential applications of distance measurements by double electron–electron resonance (DEER) pulsed EPR technique on the receptor
Neuropeptide Y receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database
Neuropeptide Y (NPY) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Neuropeptide Y Receptors [156]) are activated by the endogenous peptides neuropeptide Y, neuropeptide Y-(3-36), peptide YY, PYY-(3-36) and pancreatic polypeptide (PP). The receptor originally identified as the Y3 receptor has been identified as the CXCR4 chemokine recepter (originally named LESTR, [137]). The y6 receptor is a functional gene product in mouse, absent in rat, but contains a frame-shift mutation in primates producing a truncated non-functional gene [83]. Many of the agonists exhibit differing degrees of selectivity dependent on the species examined. For example, the potency of PP is greater at the rat Y4 receptor than at the human receptor [61]. In addition, many agonists lack selectivity for individual subtypes, but can exhibit comparable potency against pairs of NPY receptor subtypes, or have not been examined for activity at all subtypes. [125I]-PYY or [125I]-NPY can be used to label Y1, Y2, Y5 and y6 subtypes non-selectively, while [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP may be used to label Y5 receptors preferentially (note that cPP denotes chicken peptide sequence and hPP is the human sequence)
- …