QIPC

Gap scaling at Berezinskii-Kosterlitz-Thouless quantum critical points in one-dimensional Hubbard and Heisenberg models

Date: 
2014-12-17
Author(s): 

M. Dalmonte, J. Carrasquilla, L. Taddia, E. Ercolessi, M. Rigol

Reference: 

Phys. Rev. B 91, 165136 (2015)

We discuss how to locate critical points in the Berezinskii-Kosterlitz-Thouless (BKT) universality class by means of gap-scaling analyses. While accurately determining such points using gap extrapolation procedures is usually challenging and inaccurate due to the exponentially small value of the gap in the vicinity of the critical point, we show that a generic gap-scaling analysis, including the effects of logarithmic corrections, provides very accurate estimates of BKT transition points in a variety of spin and fermionic models.

Implementation of the Dicke lattice model in hybrid quantum system arrays

Date: 
2014-05-13
Author(s): 

Liujun Zou, David Marcos, Sebastian Diehl, Stefan Putz, Jörg Schmiedmayer, Johannes Majer, Peter Rabl

Reference: 

Phys. Rev. Lett. 113, 023603 (2014)

Generalized Dicke models can be implemented in hybrid quantum systems built from ensembles of nitrogen-vacancy (NV) centers in diamond coupled to superconducting microwave cavities. By engineering cavity assisted Raman transitions between two spin states of the NV defect, a fully tunable model for collective light-matter interactions in the ultra-strong coupling limit can be obtained.

Probing Entanglement in Adiabatic Quantum Optimization with Trapped Ions

Date: 
2014-11-28
Author(s): 

Philipp Hauke, Lars Bonnes, Markus Heyl, Wolfgang Lechner

Reference: 

Front. Phys. 3, 21 (2015)

Adiabatic quantum optimization has been proposed as a route to solve NP-complete problems, with a possible quantum speedup compared to classical algorithms. However, the precise role of quantum effects, such as entanglement, in these optimization protocols is still unclear. We propose a setup of cold trapped ions that allows one to quantitatively characterize, in a controlled experiment, the interplay of entanglement, decoherence, and non-adiabaticity in adiabatic quantum optimization.

Tensor Networks for Lattice Gauge Theories with continuous groups

Date: 
2014-05-19
Author(s): 

Luca Tagliacozzo, Alessio Celi, Maciej Lewenstein

Reference: 

Phys. Rev. X 4, 041024 (2014).

We discuss how to formulate lattice gauge theories in the Tensor Network language. In this way we obtain both a consistent truncation scheme of the Kogut-Susskind lattice gauge theories and a Tensor Network variational ansatz for gauge invariant states that can be used in actual numerical computation. Our construction is also applied to the simplest realization of the quantum link models/gauge magnets and provides a clear way to understand their microscopic relation with Kogut-Susskind lattice gauge theories.

Quantum Spin Ice and dimer models with Rydberg atoms

Date: 
2014-04-21
Author(s): 

Alexander W. Glaetzle, Marcello Dalmonte, Rejish Nath, Ioannis Rousochatzakis, Roderich Moessner, Peter Zoller

Reference: 

Phys. Rev. X 4, 041037 (2014).

Quantum spin ice represents a paradigmatic example on how the physics of frustrated magnets is related to gauge theories. In the present work we address the problem of approximately realizing quantum spin ice in two dimensions with cold atoms in optical lattices. The relevant interactions are obtained by weakly admixing van der Waals interactions between laser admixed Rydberg states to the atomic ground state atoms, exploiting the strong angular dependence of interactions between Rydberg p-states together with the possibility of designing step-like potentials.

Quantum computations on a topologically encoded qubit

Date: 
2016-06-07
Author(s): 

D. Nigg, M. Müller, E. A. Martinez, P. Schindler, M. Hennrich, T. Monz, M. A. Martin-Delgado, R. Blatt

Reference: 

Science 345, 302 (2014)

The construction of a quantum computer remains a fundamental scientific and technological challenge because of the influence of unavoidable noise. Quantum states and operations can be protected from errors through the use of protocols for quantum computing with faulty components. We present a quantum error-correcting code in which one qubit is encoded in entangled states distributed over seven trapped-ion qubits. The code can detect one bit flip error, one phase flip error, or a combined error of both, regardless on which of the qubits they occur.

Electromagnetically-induced-transparency ground-state cooling of long ion strings

Date: 
2016-06-07
Author(s): 

R. Lechner, C. Maier, C. Hempel, P. Jurcevic, B. P. Lanyon, T. Monz, M. Brownnutt, R. Blatt, C. F. Roos

Reference: 

Phys. Rev. A 93, 053401 (2016)

Electromagnetically-induced-transparency (EIT) cooling is a ground-state cooling technique for trapped particles. EIT offers a broader cooling range in frequency space compared to more established methods. In this work, we experimentally investigate EIT cooling in strings of trapped atomic ions. In strings of up to 18 ions, we demonstrate simultaneous ground-state cooling of all radial modes in under 1 ms. This is a particularly important capability in view of emerging quantum simulation experiments with large numbers of trapped ions.

Sympathetic cooling and detection of a hot trapped ion by a cold one

Date: 
2016-06-07
Author(s): 

M. Guggemos, D. Heinrich, O. A. Herrera-Sancho, R. Blatt, C. F. Roos

Reference: 

New J. Phys. 17, 103001 (2015)

We investigate the dynamics of an ion sympathetically cooled by another laser-cooled ion or small ion crystal. To this end, we develop simple models of the cooling dynamics in the limit of weak Coulomb interactions. Experimentally, we create a two-ion crystal of Ca+ and Al+ by photo-ionization of neutral atoms produced by laser ablation. We characterize the velocity distribution of the laser-ablated atoms crossing the trap by time-resolved fluorescence spectroscopy.

Quasiparticle engineering and entanglement propagation in a quantum many-body system

Date: 
2016-06-07
Author(s): 

P. Jurcevic, B. P. Lanyon, P. Hauke, C. Hempel, P. Zoller, R. Blatt, C. F. Roos

Reference: 

Nature 511, 202 (2014)

The key to explaining and controlling a range of quantum phenomena is to study how information propagates around many-body systems. Quantum dynamics can be described by particle-like carriers of information that emerge in the collective behaviour of the underlying system, the so-called quasiparticles1.

Tomography of band insulators from quench dynamics

Date: 
2014-01-31
Author(s): 

Philipp Hauke, Maciej Lewenstein, André Eckardt

Reference: 

Phys. Rev. Lett. 113, 045303 (2014)

We propose a simple scheme for tomography of band-insulating states in one- and two-dimensional optical lattices with two sublattice states. In particular, the scheme maps out the Berry curvature in the entire Brillouin zone and extracts topological invariants such as the Chern number. The measurement relies on observing---via time-of-flight imaging---the time evolution of the momentum distribution following a sudden quench in the band structure. We consider two examples of experimental relevance: the Harper model with π-flux and the Haldane model on a honeycomb lattice.

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