AQUTE

Effect of qubit losses on Grover's quantum search algorithm

Mon, 2013-05-06 15:33 - Mattia Giardini

Date:

2012-10-18

Author(s):

D. D. Bhaktavatsala Rao and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.86.042321
DOI: 10.1103/PhysRevA.86.042321
PACS: 03.67.Lx, 03.67.Pp, 03.65.Yz

We investigate the performance of Grover's quantum search algorithm on a register that is subject to a loss of particles that carry qubit information. Under the assumption that the basic steps of the algorithm are applied correctly on the correspondingly shrinking register, we show that the algorithm converges to mixed states with 50% overlap with the target state in the bit positions still present.

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Measurement-induced two-qubit entanglement in a bad cavity: Fundamental and practical considerations

Mon, 2013-05-06 15:27 - Mattia Giardini

Date:

2012-03-21

Author(s):

Brian Julsgaard and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.85.032327
DOI: 10.1103/PhysRevA.85.032327
PACS: 03.67.Bg, 42.50.Pq, 42.50.Lc, 03.65.Ta

An entanglement-generating protocol is described for two qubits coupled to a cavity field in the bad-cavity limit. By measuring the amplitude of a field transmitted through the cavity, an entangled spin-singlet state can be established probabilistically. Both fundamental limitations and practical measurement schemes are discussed, and the influence of dissipative processes and inhomogeneities in the qubits are analyzed.

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Qubit purification speed-up for three complementary continuous measurements

Mon, 2013-05-06 15:17 - Mattia Giardini

Date:

2012-11-28

Author(s):

Ruskov R, Combes J, Mølmer K, Wiseman HM.

Reference:

doi: 10.1098/rsta.2011.0516.

URL:

http://www.ncbi.nlm.nih.gov/pubmed/23091209

We consider qubit purification under simultaneous continuous measurement of the three non-commuting qubit operators σ(x), σ(y), σ(z). The purification dynamics is quantified by (i) the average purification rate and (ii) the mean time of reaching a given level of purity, 1-ε.

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Squeezing of collective excitations in spin ensembles

Mon, 2013-05-06 15:11 - Mattia Giardini

Date:

2012-10-22

Author(s):

Christian Kraglund Andersen and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.86.043831
DOI: 10.1103/PhysRevA.86.043831
PACS: 42.50.Pq, 42.50.Lc, 42.50.Ct, 03.67.Bg

We analyze the possibility of creating two-mode spin squeezed states of two separate spin ensembles by inverting the spins in one ensemble and allowing spin exchange between the ensembles via a near resonant cavity field. We investigate the dynamics of the system using a combination of numerical and analytic calculations, and we obtain squeezing for a wide range of parameters.

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Dynamical evolution of an inverted spin ensemble in a cavity: Inhomogeneous broadening as a stabilizing mechanism

Mon, 2013-05-06 15:08 - Mattia Giardini

Date:

2012-12-07

Author(s):

Brian Julsgaard and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.86.063810
DOI: 10.1103/PhysRevA.86.063810
PACS: 42.50.Pq, 42.50.Ct, 42.50.Nn

We study the evolution of an inverted spin ensemble coupled to a cavity. While the inversion itself presents an inherent instability in the system, the inhomogeneous broadening of spin-resonance frequencies provides a stabilizing mechanism. The detailed behavior of mean values and variances of the spin components and the cavity field is accounted for under both stable and unstable conditions.

Directional emission of single photons from small atomic samples

Mon, 2013-05-06 15:01 - Mattia Giardini

Date:

2013-02-19

Author(s):

Yevhen Miroshnychenko, Uffe V. Poulsen and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.87.023821
DOI: 10.1103/PhysRevA.87.023821
PACS: 42.50.Nn, 42.50.Ct, 42.50.Ex, 03.67.Hk

We provide a formalism to describe deterministic emission of single photons with tailored spatial and temporal profiles from a regular array of multilevel atoms. We assume that a single collective excitation is initially shared by all the atoms in a metastable atomic state and that this state is coupled by a classical laser field to an optically excited state which rapidly decays to the ground atomic state. Our model accounts for the different field polarization components via reabsorption and emission of light by the Zeeman manifold of optically excited states.

Qudit quantum computation in the Jaynes-Cummings model

Mon, 2013-05-06 14:57 - Mattia Giardini

Date:

2012-02-27

Author(s):

Brian Mischuck and Klaus Mølmer

Reference:

URL: http://link.aps.org/doi/10.1103/PhysRevA.87.022341
DOI: 10.1103/PhysRevA.87.022341
PACS: 03.67.Lx, 42.50.Dv, 03.67.Bg, 85.25.Cp

We have developed methods for performing qudit quantum computation in the Jaynes-Cummings model with the qudits residing in a finite subspace of individual harmonic oscillator modes, resonantly coupled to a spin-1/2 system.