1,559 research outputs found
State tomography of capacitively shunted phase qubits with high fidelity
We introduce a new design concept for superconducting quantum bits (qubits)
in which we explicitly separate the capacitive element from the Josephson
tunnel junction for improved qubit performance. The number of two-level systems
(TLS) that couple to the qubit is thereby reduced by an order of magnitude and
the measurement fidelity improves to 90%. This improved design enables the
first demonstration of quantum state tomography with superconducting qubits
using single shot measurements.Comment: submitted to PR
Geometry of unitary orbits of pinching operators
Let I be a symmetrically-normed ideal of the space of bounded operators acting on a Hilbert space H. Let {pi}1w(1≤w≤∞) be a family of mutually orthogonal projections on H. The pinching operator associated with the former family of projections is given by P:I→I,P(x)=∑i=1wpixpi. Let UI denote the Banach-Lie group of the unitary operators whose difference with the identity belongs to I. We study geometric properties of the orbit UI(P)={LuPLu*:u∈UI}, where Lu is the left representation of UI on the algebra B(I) of bounded operators acting on I. The results include necessary and sufficient conditions for UI(P) to be a submanifold of B(I). Special features arise in the case of the ideal K of compact operators. In general, UK(P) turns out to be a non complemented submanifold of B(K). We find a necessary and sufficient condition for UK(P) to have complemented tangent spaces in B(K). We also show that UI(P) is a covering space of another orbit of pinching operators.Facultad de Ciencias Exacta
HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7
We present HI observations of the Sculptor Group starburst spiral galaxy NGC
253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for
the SKA precursor MeerKAT, under construction. The short baselines and low
system temperature of the telescope make it very sensitive to large scale, low
surface brightness emission. The KAT-7 observations detected 33% more flux than
previous VLA observations, mainly in the outer parts and in the halo for a
total HI mass of M. HI can be found at
large distances perpendicular to the plane out to projected distances of ~9-10
kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel
technique, based on interactive profile fitting, was used to separate the main
disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the
HI disk confirms that it is declining in the outer parts, as seen in previous
optical Fabry-Perot measurements. As for the anomalous component, its RC has a
very shallow gradient in the inner parts and turns over at the same radius as
the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed
extra planar gas is compatible with an outflow due to the central starburst and
galactic fountains in the outer parts. However, the gas kinematics shows no
evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the
star formation rate (SFR) is compatible with the starburst nature of NGC 253.Comment: 18 pages, 20 figures, 8 Tables. Accepted for publication to MNRA
Computing prime factors with a Josephson phase qubit quantum processor
A quantum processor (QuP) can be used to exploit quantum mechanics to find
the prime factors of composite numbers[1]. Compiled versions of Shor's
algorithm have been demonstrated on ensemble quantum systems[2] and photonic
systems[3-5], however this has yet to be shown using solid state quantum bits
(qubits). Two advantages of superconducting qubit architectures are the use of
conventional microfabrication techniques, which allow straightforward scaling
to large numbers of qubits, and a toolkit of circuit elements that can be used
to engineer a variety of qubit types and interactions[6, 7]. Using a number of
recent qubit control and hardware advances [7-13], here we demonstrate a
nine-quantum-element solid-state QuP and show three experiments to highlight
its capabilities. We begin by characterizing the device with spectroscopy.
Next, we produces coherent interactions between five qubits and verify bi- and
tripartite entanglement via quantum state tomography (QST) [8, 12, 14, 15]. In
the final experiment, we run a three-qubit compiled version of Shor's algorithm
to factor the number 15, and successfully find the prime factors 48% of the
time. Improvements in the superconducting qubit coherence times and more
complex circuits should provide the resources necessary to factor larger
composite numbers and run more intricate quantum algorithms.Comment: 5 pages, 3 figure
Microwave Dielectric Loss at Single Photon Energies and milliKelvin Temperatures
The microwave performance of amorphous dielectric materials at very low
temperatures and very low excitation strengths displays significant excess
loss. Here, we present the loss tangents of some common amorphous and
crystalline dielectrics, measured at low temperatures (T < 100 mK) with near
single-photon excitation energies, using both coplanar waveguide (CPW) and
lumped LC resonators. The loss can be understood using a two-level state (TLS)
defect model. A circuit analysis of the half-wavelength resonators we used is
outlined, and the energy dissipation of such a resonator on a multilayered
dielectric substrate is considered theoretically.Comment: 4 pages, 3 figures, submitted to Applied Physics Letter
Essentially commuting projections
Let H=H+⊕H- be a fixed orthogonal decomposition of a Hilbert space, with both subspaces of infinite dimension, and let E+, E- be the projections onto H+ and H-. We study the set Pcc of orthogonal projections P in H which essentially commute with E+ (or equivalently with E-), i.e.[P,E+]=PE+-E+Pis compact. By means of the projection π onto the Calkin algebra, one sees that these projections P∈Pcc fall into nine classes. Four discrete classes, which correspond to π(P) being 0, 1, π(E+) or π(E-), and five essential classes which we describe below. The discrete classes are, respectively, the finite rank projections, finite co-rank projections, the Sato Grassmannian of H+ and the Sato Grassmannian of H-. Thus the connected components of each of these classes are parametrized by the integers (via de rank, the co-rank or the Fredholm index, respectively). The essential classes are shown to be connected.We are interested in the geometric structure of Pcc, being the set of selfadjoint projections of the C*-algebra Bcc of operators in B(H) which essentially commute with E+. In particular, we study the problem of existence of minimal geodesics joining two given projections in the same component. We show that the Hopf-Rinow Theorem holds in the discrete classes, but not in the essential classes. Conditions for the existence and uniqueness of geodesics in these latter classes are found.Facultad de Ciencias Exacta
Generation of Three-Qubit Entangled States using Superconducting Phase Qubits
Entanglement is one of the key resources required for quantum computation, so
experimentally creating and measuring entangled states is of crucial importance
in the various physical implementations of a quantum computer. In
superconducting qubits, two-qubit entangled states have been demonstrated and
used to show violations of Bell's Inequality and to implement simple quantum
algorithms. Unlike the two-qubit case, however, where all maximally-entangled
two-qubit states are equivalent up to local changes of basis, three qubits can
be entangled in two fundamentally different ways, typified by the states
and . Here we demonstrate the operation of three coupled
superconducting phase qubits and use them to create and measure
and states. The states are fully characterized
using quantum state tomography and are shown to satisfy entanglement witnesses,
confirming that they are indeed examples of three-qubit entanglement and are
not separable into mixtures of two-qubit entanglement.Comment: 9 pages, 5 figures. Version 2: added supplementary information and
fixed image distortion in Figure 2
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