Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions

We report on the direct observation of spin-exchanging interactions in a two-orbital SU(N)-symmetric quantum gas of ytterbium in an optical lattice. The two orbital states are represented by two different (meta-)stable electronic configurations of fermionic Yb-173. A strong spin-exchange between particles in the two separate orbitals is mediated by the contact interaction between atoms, which we characterize by clock shift spectroscopy in a 3D optical lattice. We find the system to be SU(N)-symmetric within our measurement precision and characterize all relevant scattering channels for atom pairs in combinations of the ground and the excited state. Elastic scattering between the orbitals is dominated by the antisymmetric channel, which leads to the strong spin-exchange coupling. The exchange process is directly observed, by characterizing the dynamic equilibration of spin imbalances between two large ensembles in the two orbital states, as well as indirectly in atom pairs via interaction shift spectroscopy in a 3D lattice. The realization of a stable SU(N)-symmetric two-orbital Hubbard Hamiltonian opens the route towards experimental quantum simulation of condensed-matter models based on orbital interactions, such as the Kondo lattice model.Comment: Correction: In the original version of this preprint the assignment of states with symmetric electronic wavefunction (|eg+>) and with antisymmetric electronic wavefunction (|eg->) to the observed spectral lines was inverted. This has been corrected in the current version. The results of the paper remain unchanged, with the exchange coupling being inverted to a ferromagnetic exchang

Non-equilibrium Thermodynamics of Spacetime

It has previously been shown that the Einstein equation can be derived from the requirement that the Clausius relation dS = dQ/T hold for all local acceleration horizons through each spacetime point, where dS is one quarter the horizon area change in Planck units, and dQ and T are the energy flux across the horizon and Unruh temperature seen by an accelerating observer just inside the horizon. Here we show that a curvature correction to the entropy that is polynomial in the Ricci scalar requires a non-equilibrium treatment. The corresponding field equation is derived from the entropy balance relation dS =dQ/T+dS_i, where dS_i is a bulk viscosity entropy production term that we determine by imposing energy-momentum conservation. Entropy production can also be included in pure Einstein theory by allowing for shear viscosity of the horizon.Comment: 4 pages. Dedicated to Rafael Sorkin on the occasion of his 60th birthda

Depletion isolation effect in Vertical MOSFETS during transition from partial to fully depleted operation

A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200–60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drain–current is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60–10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gate–gate coupling contribute to the drain–current for pillar thicknesses between 100–40 nm

Selective darkening of degenerate transitions for implementing quantum controlled-NOT gates

We present a theoretical analysis of the selective darkening method for implementing quantum controlled-NOT (CNOT) gates. This method, which we recently proposed and demonstrated, consists of driving two transversely-coupled quantum bits (qubits) with a driving field that is resonant with one of the two qubits. For specific relative amplitudes and phases of the driving field felt by the two qubits, one of the two transitions in the degenerate pair is darkened, or in other words, becomes forbidden by effective selection rules. At these driving conditions, the evolution of the two-qubit state realizes a CNOT gate. The gate speed is found to be limited only by the coupling energy J, which is the fundamental speed limit for any entangling gate. Numerical simulations show that at gate speeds corresponding to 0.48J and 0.07J, the gate fidelity is 99% and 99.99%, respectively, and increases further for lower gate speeds. In addition, the effect of higher-lying energy levels and weak anharmonicity is studied, as well as the scalability of the method to systems of multiple qubits. We conclude that in all these respects this method is competitive with existing schemes for creating entanglement, with the added advantages of being applicable for qubits operating at fixed frequencies (either by design or for exploitation of coherence sweet-spots) and having the simplicity of microwave-only operation.Comment: 25 pages, 5 figure

Partial-measurement back-action and non-classical weak values in a superconducting circuit

We realize indirect partial measurement of a transmon qubit in circuit quantum electrodynamics by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allows tailoring the measurement strength and operator. The tradeoff between measurement strength and qubit back-action is characterized through the distortion of a qubit Rabi oscillation imposed by ancilla measurement in different bases. Combining partial and projective qubit measurements, we provide the solid-state demonstration of the correspondence between a non-classical weak value and the violation of a Leggett-Garg inequality.Comment: 5 pages, 4 figures, and Supplementary Information (8 figures

Dust absorption and scattering in the silicon K-edge

The composition and properties of interstellar silicate dust are not well understood. In X-rays, interstellar dust can be studied in detail by making use of the fine structure features in the Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearing dust, such as investigating the crystallinity, abundance, and the chemical composition along a given line of sight. We present newly acquired laboratory measurements of the silicon K-edge of several silicate-compounds that complement our measurements from our earlier pilot study. The resulting dust extinction profiles serve as templates for the interstellar extinction that we observe. The extinction profiles were used to model the interstellar dust in the dense environments of the Galaxy. The laboratory measurements, taken at the Soleil synchrotron facility in Paris, were adapted for astrophysical data analysis and implemented in the SPEX spectral fitting program. The models were used to fit the spectra of nine low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. Most lines of sight can be fit well by amorphous olivine. We also established upper limits on the amount of crystalline material that the modeling allows. We obtained values of the total silicon abundance, silicon dust abundance, and depletion along each of the sightlines. We find a possible gradient of $0.06\pm0.02$ dex/kpc for the total silicon abundance versus the Galactocentric distance. We do not find a relation between the depletion and the extinction along the line of sight.Comment: 18 pages, 16 figures. Accepted for publication in Astronomy and Astrophysic

Low-crosstalk bifurcation detectors for coupled flux qubits

We present experimental results on the crosstalk between two AC-operated dispersive bifurcation detectors, implemented in a circuit for high-fidelity readout of two strongly coupled flux qubits. Both phase-dependent and phase-independent contributions to the crosstalk are analyzed. For proper tuning of the phase the measured crosstalk is 0.1 % and the correlation between the measurement outcomes is less than 0.05 %. These results show that bifurcative readout provides a reliable and generic approach for multi-partite correlation experiments.Comment: Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at http://link.aip.org/link/?apl/96/12350

H-theorem for classical matter around a black hole

We propose a classical solution for the kinetic description of matter falling into a black hole, which permits to evaluate both the kinetic entropy and the entropy production rate of classical infalling matter at the event horizon. The formulation is based on a relativistic kinetic description for classical particles in the presence of an event horizon. An H-theorem is established which holds for arbitrary models of black holes and is valid also in the presence of contracting event horizons