735 research outputs found
Quantum dynamics of a dc-SQUID coupled to an asymmetric Cooper pair transistor
We present a theoretical analysis of the quantum dynamics of a
superconducting circuit based on a highly asymmetric Cooper pair transistor
(ACPT) in parallel to a dc-SQUID. Starting from the full Hamiltonian we show
that the circuit can be modeled as a charge qubit (ACPT) coupled to an
anharmonic oscillator (dc-SQUID). Depending on the anharmonicity of the SQUID,
the Hamiltonian can be reduced either to one that describes two coupled qubits
or to the Jaynes-Cummings Hamiltonian. Here the dc-SQUID can be viewed as a
tunable micron-size resonator. The coupling term, which is a combination of a
capacitive and a Josephson coupling between the two qubits, can be tuned from
the very strong- to the zero-coupling regimes. It describes very precisely the
tunable coupling strength measured in this circuit and explains the
'quantronium' as well as the adiabatic quantum transfer read-out.Comment: 20 page
A V-shape superconducting artificial atom based on two inductively coupled transmons
Circuit quantum electrodynamics systems are typically built from resonators
and two-level artificial atoms, but the use of multi-level artificial atoms
instead can enable promising applications in quantum technology. Here we
present an implementation of a Josephson junction circuit dedicated to operate
as a V-shape artificial atom. Based on a concept of two internal degrees of
freedom, the device consists of two transmon qubits coupled by an inductance.
The Josephson nonlinearity introduces a strong diagonal coupling between the
two degrees of freedom that finds applications in quantum non-demolition
readout schemes, and in the realization of microwave cross-Kerr media based on
superconducting circuits.Comment: 5 pages, 3 figure
Experimental demonstration of Aharonov-Casher interference in a Josephson junction circuit
A neutral quantum particle with magnetic moment encircling a static electric
charge acquires a quantum mechanical phase (Aharonov-Casher effect). In
superconducting electronics the neutral particle becomes a fluxon that moves
around superconducting islands connected by Josephson junctions. The full
understanding of this effect in systems of many junctions is crucial for the
design of novel quantum circuits. Here we present measurements and quantitative
analysis of fluxon interference patterns in a six Josephson junction chain. In
this multi-junction circuit the fluxon can encircle any combination of charges
on five superconducting islands, resulting in a complex pattern. We compare the
experimental results with predictions of a simplified model that treats fluxons
as independent excitations and with the results of the full diagonalization of
the quantum problem. Our results demonstrate the accuracy of the fluxon
interference description and the quantum coherence of these arrays
The Domination Number of Grids
In this paper, we conclude the calculation of the domination number of all
grid graphs. Indeed, we prove Chang's conjecture saying that for
every , .Comment: 12 pages, 4 figure
Strong tunable coupling between a superconducting charge and phase qubit
We have realized a tunable coupling over a large frequency range between an
asymmetric Cooper pair transistor (charge qubit) and a dc SQUID (phase qubit).
Our circuit enables the independent manipulation of the quantum states of each
qubit as well as their entanglement. The measurements of the charge qubit's
quantum states is performed by resonant read-out via the measurement of the
quantum states of the SQUID. The measured coupling strength is in agreement
with an analytic theory including a capacitive and a tunable Josephson coupling
between the two qubits.Comment: 5 page
Fast high fidelity quantum non-demolition qubit readout via a non-perturbative cross-Kerr coupling
Qubit readout is an indispensable element of any quantum information
processor. In this work, we experimentally demonstrate a non-perturbative
cross-Kerr coupling between a transmon and a polariton mode which enables an
improved quantum non-demolition (QND) readout for superconducting qubits. The
new mechanism uses the same experimental techniques as the standard QND qubit
readout in the dispersive approximation, but due to its non-perturbative
nature, it maximizes the speed, the single-shot fidelity and the QND properties
of the readout. In addition, it minimizes the effect of unwanted decay channels
such as the Purcell effect. We observed a single-shot readout fidelity of 97.4%
for short 50 ns pulses, and we quantified a QND-ness of 99% for long
measurement pulses with repeated single-shot readouts
Fabrication of stable and reproducible sub-micron tunnel junctions
We have performed a detailed study of the time stability and reproducibility
of sub-micron tunnel junctions, fabricated using standard
double angle shadow evaporations. We have found that by aggressively cleaning
the substrate before the evaporations, thus preventing any contamination of the
junction, we obtained perfectly stable oxide barriers. We also present
measurements on large ensembles of junctions which prove the reproducibility of
the fabrication process. The measured tunnel resistance variance in large
ensembles of identically fabricated junctions is in the range of only a few
percents. Finally, we have studied the effect of different thermal treatments
on the junction barrier. This is especially important for multiple step
fabrication processes which imply annealing the junction.Comment: 4 pages, 3 figure
Coherent frequency conversion in a superconducting artificial atom with two internal degrees of freedom
By adding a large inductance in a dc-SQUID phase qubit loop, one decouples
the junctions' dynamics and creates a superconducting artificial atom with two
internal degrees of freedom. In addition to the usual symmetric plasma mode
({\it s}-mode) which gives rise to the phase qubit, an anti-symmetric mode
({\it a}-mode) appears. These two modes can be described by two anharmonic
oscillators with eigenstates and for the {\it s}
and {\it a}-mode, respectively. We show that a strong nonlinear coupling
between the modes leads to a large energy splitting between states
and . Finally, coherent frequency
conversion is observed via free oscillations between the states
and
Qubit readout using in-situ bifurcation of a nonlinear dissipative polariton in the mesoscopic regime
We explore the nonlinear response to a strong drive of polaritonic meters for
superconducting qubit state readout. The two polaritonic meters result from the
strong hybridization between a bosonic mode of a 3D microwave cavity and an
anharmonic ancilla mode of the superconducting circuit. Both polaritons inherit
a self-Kerr nonlinearity , and decay rate from the ancilla and
cavity, respectively. They are coupled to a transmon qubit via a
non-perturbative cross-Kerr coupling resulting in a large cavity pull . By applying magnitic flux, the ancilla mode frequency varies
modifying the hybridization conditions and thus the properties of the readout
polariton modes. Using this, the hybridisation is tuned in the mesoscopic
regime of the non-linear dissipative polariton where the self-Kerr and decay
rates of one polariton are similar leading to bistability and
bifurcation behavior at small photon number. This bistability and bifurcation
behavior depends on the qubit state and we report qubit state readout in a
latching-like manner thanks to the bifurcation of the upper polariton. Without
any external quantum-limited amplifier, we obtain a single-shot fidelity of
in a ns integration time
Early Science with the Large Millimeter Telescope: an energy-driven wind revealed by massive molecular and fast X-ray outflows in the Seyfert Galaxy IRAS 17020+4544
We report on the coexistence of powerful gas outflows observed in millimeter
and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544.
Thanks to the large collecting power of the Large Millimeter Telescope, a
prominent line arising from the 12CO(1-0) transition was revealed in recent
observations of this source. The complex profile is composed by a narrow
double-peak line and a broad wing. While the double-peak structure may be
arising in a disk of molecular material, the broad wing is interpreted as the
signature of a massive outflow of molecular gas with an approximate bulk
velocity of -660 km/s. This molecular wind is likely associated to a
multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c
and column densities in the range 10^{21-23.9} cm^-2 that was reported in the
source prior to the LMT observations. The momentum load estimated in the two
gas phases indicates that within the observational uncertainties the outflow is
consistent with being propagating through the galaxy and sweeping up the gas
while conserving its energy. This scenario, which has been often postulated as
a viable mechanism of how AGN feedback takes place, has so far been observed
only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity
respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example
of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary
multi-wavelength data recently obtained on this source will allow us to
corroborate the proposed hypothesis.Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figure
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