2,108 research outputs found
Superconducting quantum node for entanglement and storage of microwave radiation
Superconducting circuits and microwave signals are good candidates to realize
quantum networks, which are the backbone of quantum computers. We have realized
a quantum node based on a 3D microwave superconducting cavity parametrically
coupled to a transmission line by a Josephson ring modulator. We first
demonstrate the time-controlled capture, storage and retrieval of an optimally
shaped propagating microwave field, with an efficiency as high as 80%. We then
demonstrate a second essential ability, which is the timed-controlled
generation of an entangled state distributed between the node and a microwave
channel.Comment: 6 pages, 4 figures. Supplementary information can be downloaded as
the ancillary file her
Quantum trajectories and their statistics for remotely entangled quantum bits
We experimentally and theoretically investigate the quantum trajectories of
jointly monitored transmon qubits embedded in spatially separated microwave
cavities. Using nearly quantum-noise limited superconducting amplifiers and an
optimized setup to reduce signal loss between cavities, we can efficiently
track measurement-induced entanglement generation as a continuous process for
single realizations of the experiment. The quantum trajectories of transmon
qubits naturally split into low and high entanglement classes corresponding to
half-parity collapse. The distribution of concurrence is found at any given
time and we explore the dynamics of entanglement creation in the state space.
The distribution exhibits a sharp cut-off in the high concurrence limit,
defining a maximal concurrence boundary. The most likely paths of the qubits'
trajectories are also investigated, resulting in three probable paths,
gradually projecting the system to two even subspaces and an odd subspace. We
also investigate the most likely time for the individual trajectories to reach
their most entangled state, and find that there are two solutions for the local
maximum, corresponding to the low and high entanglement routes. The theoretical
predictions show excellent agreement with the experimental entangled qubit
trajectory data.Comment: 11 pages and 4 figure
Propagating Polaritons in III-Nitride Slab Waveguides
We report on III-nitride waveguides with c-plane GaN/AlGaN quantum wells in
the strong light-matter coupling regime supporting propagating polaritons. They
feature a normal mode splitting as large as 60 meV at low temperatures thanks
to the large overlap between the optical mode and the active region, a
polariton decay length up to 100 m for photon-like polaritons and lifetime
of 1-2 ps; with the latter values being essentially limited by residual
absorption occurring in the waveguide. The fully lattice-matched nature of the
structure allows for very low disorder and high in-plane homogeneity; an
important asset for the realization of polaritonic integrated circuits that
could support nonlinear polariton wavepackets up to room temperature thanks to
the large exciton binding energy of 40 meV
Stabilizing Spin Coherence Through Environmental Entanglement in Strongly Dissipative Quantum Systems
The key feature of a quantum spin coupled to a harmonic bath---a model
dissipative quantum system---is competition between oscillator potential energy
and spin tunneling rate. We show that these opposing tendencies cause
environmental entanglement through superpositions of adiabatic and
antiadiabatic oscillator states, which then stabilizes the spin coherence
against strong dissipation. This insight motivates a fast-converging
variational coherent-state expansion for the many-body ground state of the
spin-boson model, which we substantiate via numerical quantum tomography.Comment: 5 pages, 3 figures, supplementary file attached. This article
supersedes arXiv:1301.743
Surface Loving and Surface Avoiding modes
We theoretically study the propagation of sound waves in GaAs/AlAs
superlattices focussing on periodic modes in the vicinity of the band gaps.
Based on analytical and numerical calculations, we show that these modes are
the product of a quickly oscillating function times a slowly varying envelope
function. We carefully study the phase of the envelope function compared to the
surface of a semi-infinite superlattice. Especially, the dephasing of the
superlattice compared to its surface is a key parameter. We exhibit two kind of
modes: Surface Avoiding and Surface Loving Modes whose envelope functions have
their minima and respectively maxima in the vicinity of the surface. We finally
consider the observability of such modes. While Surface avoiding modes have
experimentally been observed (Phys. Rev. Lett. 97, 1224301 (2006)), we show
that Surface Loving Modes are likely to be observable and we discuss the
achievement of such experiments. The proposed approach could be easily
transposed to other types of wave propagation in unidimensional semi-infinite
periodic structures as photonic Bragg mirror.Comment: 12 pages, 9 figure
Gold-catalyzed synthesis of enantioenriched furfurylamines from amino acids
International audienceA convenient gold-catalyzed asymmetric synthesis of polysubstituted furfurylamines starting from amino acids has been achieved. The cyclization proceeded under mild conditions and generally provided the furan or iodofuran derivatives in good to excellent yields and with high enantiomeric excess. Iodofurans were validated as good intermediates for classical organometallic coupling reactions
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
Comparison between hybrid and fully kinetic models of asymmetric magnetic reconnection: coplanar and guide field configurations
Magnetic reconnection occurring in collisionless environments is a
multi-scale process involving both ion and electron kinetic processes. Because
of their small mass, the electron scales are difficult to resolve in numerical
and satellite data, it is therefore critical to know whether the overall
evolution of the reconnection process is influenced by the kinetic nature of
the electrons, or is unchanged when assuming a simpler, fluid, electron model.
This paper investigate this issue in the general context of an asymmetric
current sheet, where both the magnetic field amplitude and the density vary
through the discontinuity. A comparison is made between fully kinetic and
hybrid kinetic simulations of magnetic reconnection in coplanar and guide field
systems. The models share the initial condition but differ in their electron
modeling. It is found that the overall evolution of the system, including the
reconnection rate, is very similar between both models. The best agreement is
found in the guide field system, which confines particle better than the
coplanar one, where the locality of the moments is violated by the electron
bounce motion. It is also shown that, contrary to the common understanding,
reconnection is much faster in the guide field system than in the coplanar one.
Both models show this tendency, indicating that the phenomenon is driven by ion
kinetic effects and not electron ones.Comment: 11 pages, 8 figures, accepted in Physics of Plasma
Persistent control of a superconducting qubit by stroboscopic measurement feedback
Making a system state follow a prescribed trajectory despite fluctuations and
errors commonly consists in monitoring an observable (temperature,
blood-glucose level...) and reacting on its controllers (heater power, insulin
amount ...). In the quantum domain, there is a change of paradigm in feedback
since measurements modify the state of the system, most dramatically when the
trajectory goes through superpositions of measurement eigenstates. Here, we
demonstrate the stabilization of an arbitrary trajectory of a superconducting
qubit by measurement based feedback. The protocol benefits from the long
coherence time (s) of the 3D transmon qubit, the high efficiency
(82%) of the phase preserving Josephson amplifier, and fast electronics
ensuring less than 500 ns delay. At discrete time intervals, the state of the
qubit is measured and corrected in case an error is detected. For Rabi
oscillations, where the discrete measurements occur when the qubit is supposed
to be in the measurement pointer states, we demonstrate an average fidelity of
85% to the targeted trajectory. For Ramsey oscillations, which does not go
through pointer states, the average fidelity reaches 75%. Incidentally, we
demonstrate a fast reset protocol allowing to cool a 3D transmon qubit down to
0.6% in the excited state.Comment: 7 pages, 3 figures and 1 table. Supplementary information available
as an ancilla fil
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