52 research outputs found
Unexpectedly allowed transition in two inductively coupled transmons
We present experimental results in which the unexpected zero-two transition
of a circuit composed of two inductively coupled transmons is observed. This
transition shows an unusual magnetic flux dependence with a clear disappearance
at zero magnetic flux. In a transmon qubit the symmetry of the wave functions
prevents this transition to occur due to selection rule. In our circuit the
Josephson effect introduces strong couplings between the two normal modes of
the artificial atom. This leads to a coherent superposition of states from the
two modes enabling such transitions to occur
Kerr coefficients of plasma resonances in Josephson junction chains
We present an experimental and theoretical analysis of the self- and
cross-Kerr effect of extended plasma resonances in Josephson junction chains.
We calculate the Kerr coefficients by deriving and diagonalizing the
Hamiltonian of a linear circuit model for the chain and then adding the
Josephson non-linearity as a perturbation. The calculated Kerr-coefficients are
compared with the measurement data of a chain of 200 junctions. The Kerr effect
manifests itself as a frequency shift that depends linearly on the number of
photons in a resonant mode. By changing the input power on a low signal level,
we are able to measure this shift. The photon number is calibrated using the
self-Kerr shift calculated from the sample parameters. We then compare the
measured cross-Kerr shift with the theoretical prediction, using the calibrated
photon number.Comment: 10 pages, 9 figure
Evidence of dual Shapiro steps in a Josephson junctions array
The modern primary voltage standard is based on the AC Josephson effect and
the ensuing Shapiro steps, where a microwave tone applied to a Josephson
junction yields a constant voltage ( is Planck's constant and
the electron charge) determined by only the microwave frequency and
fundamental constants. Duality arguments for current and voltage have long
suggested the possibility of dual Shapiro steps -- that a Josephson junction
device could produce current steps with heights determined only on the applied
frequency. In this report, we embed an ultrasmall Josephson junction in a high
impedance array of larger junctions to reveal dual Shapiro steps. For multiple
frequencies, we detect that the AC response of the circuit is synchronised with
the microwave tone at frequency , and the corresponding emergence of flat
steps in the DC response with current , equal to the tunnelling of a
Cooper pair per tone period. This work sheds new light on phase-charge duality,
omnipresent in condensed matter physics, and extends it to Josephson circuits.
Looking forward, it opens a broad range of possibilities for new experiments in
the field of circuit quantum electrodynamics and is an important step towards
the long-sought closure of the quantum metrology electrical triangle.Comment: 14 pages, 11 figure
Electronic structure of epitaxial graphene layers on SiC: effect of the substrate
Recent transport measurements on thin graphite films grown on SiC show large
coherence lengths and anomalous integer quantum Hall effects expected for
isolated graphene sheets. This is the case eventhough the layer-substrate
epitaxy of these films implies a strong interface bond that should induce
perturbations in the graphene electronic structure. Our DFT calculations
confirm this strong substrate-graphite bond in the first adsorbed carbon layer
that prevents any graphitic electronic properties for this layer. However, the
graphitic nature of the film is recovered by the second and third absorbed
layers. This effect is seen in both the (0001)and 4H SiC
surfaces. We also present evidence of a charge transfer that depends on the
interface geometry. It causes the graphene to be doped and gives rise to a gap
opening at the Dirac point after 3 carbon layers are deposited in agreement
with recent ARPES experiments (T.Ohta et al, Science {\bf 313} (2006) 951)
Revealing the finite-frequency response of a bosonic quantum impurity
Quantum impurities are ubiquitous in condensed matter physics and constitute
the most stripped-down realization of many-body problems. While measuring their
finite-frequency response could give access to key characteristics such as
excitations spectra or dynamical properties, this goal has remained elusive
despite over two decades of studies in nanoelectronic quantum dots. Conflicting
experimental constraints of very strong coupling and large measurement
bandwidths must be met simultaneously. We get around this problem using cQED
tools, and build a precisely characterized quantum simulator of the boundary
sine-Gordon model, a non-trivial bosonic impurity problem. We succeeded to
fully map out the finite frequency linear response of this system. Its reactive
part evidences a strong renormalisation of the nonlinearity at the boundary in
agreement with non-perturbative calculations. Its dissipative part reveals a
dramatic many-body broadening caused by multi-photon conversion. The
experimental results are matched quantitatively to a resummed diagrammatic
calculation based on a microscopically calibrated model. Furthermore, we push
the device into a regime where diagrammatic calculations break down, which
calls for more advanced theoretical tools to model many-body quantum circuits.
We also critically examine the technological limitations of cQED platforms to
reach universal scaling laws. This work opens exciting perspectives for the
future such as quantifying quantum entanglement in the vicinity of a quantum
critical point or accessing the dynamical properties of non-trivial many-body
problems.Comment: 39 pages, 14 figure
Observation of two-mode squeezing in a traveling wave parametric amplifier
Traveling wave parametric amplifiers (TWPAs) have recently emerged as
essential tools for broadband near quantum-limited amplification. However,
their use to generate microwave quantum states still misses an experimental
demonstration. In this letter, we report operation of a TWPA as a source of
two-mode squeezed microwave radiation. We demonstrate broadband entanglement
generation between two modes separated by up to 400 MHz by measuring
logarithmic negativity between 0.27 and 0.51 and collective quadrature
squeezing below the vacuum limit between 1.5 and 2.1 dB. This work opens
interesting perspectives for the exploration of novel microwave photonics
experiments with possible applications in quantum sensing and continuous
variable quantum computing
Effects of sodium nitrite reduction, removal or replacement on cured and cooked meat for microbiological growth, food safety, colon ecosystem, and colorectal carcinogenesis in Fischer 344 rats
Epidemiological and experimental evidence indicated that processed meat consumption is associated with colorectal cancer risks. Several studies suggest the involvement of nitrite or nitrate additives via N-nitroso-compound formation (NOCs). Compared to the reference level (120 mg/kg of ham), sodium nitrite removal and reduction (90 mg/kg) similarly decreased preneoplastic lesions in F344 rats, but only reduction had an inhibitory effect on Listeria monocytogenes growth comparable to that obtained using the reference nitrite level and an effective lipid peroxidation control. Among the three nitrite salt alternatives tested, none of them led to a significant gain when compared to the reference level: vegetable stock, due to nitrate presence, was very similar to this reference nitrite level, yeast extract induced a strong luminal peroxidation and no decrease in preneoplastic lesions in rats despite the absence of NOCs, and polyphenol rich extract induced the clearest downward trend on preneoplastic lesions in rats but the concomitant presence of nitrosyl iron in feces. Except the vegetable stock, other alternatives were less efficient than sodium nitrite in reducing L. monocytogenes growth
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