References of "Martin, John"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailAnticoherence measures for pure spin states
Baguette, Dorian ULiege; Martin, John ULiege

in Physical Review A (2017), 96

The set of pure spin states with vanishing spin expectation value can be regarded as the set of the less coherent pure spin states. This set can be divided into a finite number of nested subsets on the ... [more ▼]

The set of pure spin states with vanishing spin expectation value can be regarded as the set of the less coherent pure spin states. This set can be divided into a finite number of nested subsets on the basis of higher order moments of the spin operators. This subdivision relies on the notion of anticoherent spin state to order t : A spin state is said to be anticoherent to order t if the moment of order k of the spin components along any directions are equal for k = 1,2, . . . ,t . Most spin states are neither coherent nor anticoherent, but can be arbitrary close to one or the other. In or- der to quantify the degree of anticoherence of pure spin states, we introduce the notion of anticoherence measures. By relying on the mapping between spin-j states and symmetric states of 2j spin 1/2 (Majorana representation), we present a systematic way of constructing anticoherence measures to any order. We briefly discuss their connection with measures of quantum coherence. Finally, we illustrate our measures on various spin states and use them to investigate the problem of the existence of anticoherent spin states with degenerated Majorana points. [less ▲]

Detailed reference viewed: 27 (0 ULiège)
Full Text
Peer Reviewed
See detailGenuinely entangled symmetric states with no N-partite correlations
Designolle; Giraud, Olivier; Martin, John ULiege

in Physical Review A (2017), 96

We investigate genuinely entangled N-qubit states with no N-partite correlations in the case of symmetric states. Using a tensor representation for mixed symmetric states, we obtain a simple ... [more ▼]

We investigate genuinely entangled N-qubit states with no N-partite correlations in the case of symmetric states. Using a tensor representation for mixed symmetric states, we obtain a simple characterization of the absence of N-partite correlations. We show that symmetric states with no N-partite correlations cannot exist for an even number of qubits. We fully identify the set of genuinely entangled symmetric states with no N-partite correlations in the case of three qubits, and in the case of rank-2 states. We present a general procedure to construct families for an arbitrary odd number of qubits. [less ▲]

Detailed reference viewed: 21 (0 ULiège)
Full Text
Peer Reviewed
See detailTwo-qubit entangling gates between distant atomic qubits in a lattice
Cesa, Alexandre ULiege; Martin, John ULiege

in Physical Review A (2017), 95

Arrays of qubits encoded in the ground-state manifold of neutral atoms trapped in optical (or magnetic) lattices appear to be a promising platform for the realization of a scalable quantum computer. Two ... [more ▼]

Arrays of qubits encoded in the ground-state manifold of neutral atoms trapped in optical (or magnetic) lattices appear to be a promising platform for the realization of a scalable quantum computer. Two-qubit conditional gates between nearest-neighbor qubits in the array can be implemented by exploiting the Rydberg blockade mechanism, as was shown by D. Jaksch et al. [Phys. Rev. Lett. 85, 2208 (2000)]. However, the energy shift due to dipole-dipole interactions causing the blockade falls off rapidly with the interatomic distance, and protocols based on direct Rydberg blockade typically fail to operate between atoms separated by more than one lattice site. In this work, we propose an extension of the protocol of Jaksch et al. for controlled-Z and controlled-NOT gates which works in the general case where the qubits are not nearest neighbors in the array. Our proposal relies on the Rydberg excitation hopping along a chain of ancilla noncoding atoms connecting the qubits on which the gate is to be applied. The dependence of the gate fidelity on the number of ancilla atoms, the blockade strength, and the decay rates of the Rydberg states is investigated. A comparison between our implementation of a distant controlled-NOT gate and one based on a sequence of nearest-neighbor two-qubit gates is also provided. [less ▲]

Detailed reference viewed: 42 (10 ULiège)
Full Text
Peer Reviewed
See detailScaling Theory of the Anderson Transition in Random Graphs: Ergodicity and Universality
Garcia-Mata, Ignacio; Giraud, Olivier; Georgeot, Bertrand et al

in Physical Review Letters (2017), 118

We study the Anderson transition on a generic model of random graphs with a tunable branching parameter 1 < K < 2, through large scale numerical simulations and finite-size scaling analysis. We find that ... [more ▼]

We study the Anderson transition on a generic model of random graphs with a tunable branching parameter 1 < K < 2, through large scale numerical simulations and finite-size scaling analysis. We find that a single transition separates a localized phase from an unusual delocalized phase that is ergodic at large scales but strongly nonergodic at smaller scales. In the critical regime, multifractal wave functions are located on a few branches of the graph. Different scaling laws apply on both sides of the transition: a scaling with the linear size of the system on the localized side, and an unusual volumic scaling on the delocalized side. The critical scalings and exponents are independent of the branching parameter, which strongly supports the universality of our results. [less ▲]

Detailed reference viewed: 24 (4 ULiège)
Full Text
Peer Reviewed
See detailLong-range Rydberg-blockade entangling gate mediated by auxiliary atoms
Cesa, Alexandre ULiege; Martin, John ULiege

Poster (2017, March 09)

Arrays of qubits encoded in the ground state manifold of trapped neutral atoms appear as a promising platform for the realisation of a scalable quantum computer. Indeed, such physical qubits have a long ... [more ▼]

Arrays of qubits encoded in the ground state manifold of trapped neutral atoms appear as a promising platform for the realisation of a scalable quantum computer. Indeed, such physical qubits have a long coherence time and allow for high-fidelity single-qubit operations [1]. In such a platform, entangling two-qubit gates can be implemented by exploiting the Rydberg-blockade mechanism to produce a phase shift or a flip of the state of a target atom conditioned on the state of a control atom [2]. However, because dipole-dipole interactions fall off rapidly with the interatomic distance, such entangling gates based on Rydberg-blockade are impractical between distant qubits. In this work, we propose a protocol to implement long-range Rydberg-blockade gates (CZ or CNot) using auxillary non-coding atoms to transfer the Rydberg excitation from the control to the target qubit. The dependence of the fidelity on the number of auxillary atoms, the blockade strength and the decay rates of the Rydberg states are determined. When compared to a sequential application of nearest neighbours entangling gates, our protocol leads to a larger fidelity and a reduction of the overall gate duration (which scales linearly with the number of auxillary atoms). [1] M. Saffman, J. Phys. B: At. Mol. Opt. Phys. 49, 202001 (2016). [2] D. Jaksch, J. I. Cirac, P. Zoller, S. L. Rolston, R. Côté, and M. D. Lukin, Phys. Rev. Lett. 85, 2208 (2000). [less ▲]

Detailed reference viewed: 37 (4 ULiège)
Full Text
Peer Reviewed
See detailAnticoherence measures for spin states
Baguette, Dorian ULiege; Martin, John ULiege

Poster (2017, March 09)

Among all possible spin states, spin-coherent states are the most classical because the spin expectation value in these states yields a vector of maximal norm pointing in a well defined direction. In ... [more ▼]

Among all possible spin states, spin-coherent states are the most classical because the spin expectation value in these states yields a vector of maximal norm pointing in a well defined direction. In contrast, anticoherent spin state to order t are such that <(J.n)^k> is independent of the unit vector n for k = 1, ..., t [1]. By construction, coherent and anticoherent spin states are at both ends of the spectrum of classicality. The aim of this work is to position all possible spin states on such a spectrum, that is to provide measures of anticoherence. To this aim, we introduce an axiomatic definition of anticoherence measures to any order t. In particular, we show that the total variance of a pure spin state, first introduced in [2] can be used to define a measure of anticoherence to order 1. We describe a systematic way of constructing anticoherence measures to any order that relies on the mapping between spin-j states and symmetric states of N = 2j spin-1/2. In particular, we exploit the fact that anticoherent spin states to order t have maximally mixed t-spin-1/2 reduced density matrices in the symmetric subspace [3]. [1] J. Zimba, Electron. J. Theor. Phys. 3, 143 (2006). [2] A. A. Klyachko, B. Öztop, and A. S. Shumovsky, Phys. Rev. A 75, 032315 (2007). [3] D. Baguette, T. Bastin, and J. Martin, Phys. Rev A 90, 032314 (2014). [less ▲]

Detailed reference viewed: 40 (8 ULiège)
Full Text
Peer Reviewed
See detailCompetition between finite-size effects and dipole–dipole interactions in few-atom systems
Damanet, François ULiege; Martin, John ULiege

in Journal of Physics : B Atomic Molecular & Optical Physics (2016), 49

In this paper, we study the competition between finite-size effects (i.e. discernibility of particles) and dipole–dipole interactions in few-atom systems coupled to the electromagnetic field in vacuum. We ... [more ▼]

In this paper, we study the competition between finite-size effects (i.e. discernibility of particles) and dipole–dipole interactions in few-atom systems coupled to the electromagnetic field in vacuum. We consider two hallmarks of cooperative effects, superradiance and subradiance, and compute for each the rate of energy radiated by the atoms and the coherence of the atomic state during the time evolution. We adopt a statistical approach in order to extract the typical behaviour of the atomic dynamics and average over random atomic distributions in spherical containers with prescribed k0 R with k0 the radiation wavenumber and R the average interatomic distance. Our approach allows us to highlight the tradeoff between finite-size effects and dipole– dipole interactions in superradiance/subradiance. In particular, we show the existence of an optimal value of k0R for which the superradiant intensity and coherence pulses are the less affected by dephasing effects induced by dipole–dipole interactions and finite-size effects. [less ▲]

Detailed reference viewed: 22 (2 ULiège)
Full Text
Peer Reviewed
See detailChaotic Bohmian trajectories for stationary states
Cesa, Alexandre ULiege; Martin, John ULiege; Struyve, Ward

in Journal of Physics A: Mathematical and Theoretical (2016), 49

In Bohmian mechanics, the nodes of the wave function play an important role in the generation of chaos. However, so far, most of the attention has been on moving nodes; little is known about the ... [more ▼]

In Bohmian mechanics, the nodes of the wave function play an important role in the generation of chaos. However, so far, most of the attention has been on moving nodes; little is known about the possibility of chaos in the case of stationary nodes. We address this question by considering stationary states, which provide the simplest examples of wave functions with stationary nodes. We provide examples of stationary wave functions for which there is chaos, as demonstrated by numerical computations, for one particle moving in 3 spatial dimensions and for two and three entangled particles in two dimensions. Our conclusion is that the motion of the nodes is not necessary for the generation of chaos. What is important is the overall complexity of the wave function. That is, if the wave function, or rather its phase, has complex spatial variations, it will lead to complex Bohmian trajectories and hence to chaos. Another aspect of our work concerns the average Lyapunov exponent, which quantifies the overall amount of chaos. Since it is very hard to evaluate the average Lyapunov exponent analytically, which is often computed numerically, it is useful to have simple quantities that agree well with the average Lyapunov exponent. We investigate possible correlations with quantities such as the participation ratio and different measures of entanglement, for different systems and different families of stationary wave functions. We find that these quantities often tend to correlate to the amount of chaos. However, the correlation is not perfect, because, in particular, these measures do not depend on the form of the basis states used to expand the wave function, while the amount of chaos does. [less ▲]

Detailed reference viewed: 27 (6 ULiège)
Full Text
Peer Reviewed
See detailCooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

in Physical Review A (2016), 94

We investigate superradiance and subradiance of indistinguishable atoms with quantized motional states, starting with an initial total state that factorizes over the internal and external degrees of ... [more ▼]

We investigate superradiance and subradiance of indistinguishable atoms with quantized motional states, starting with an initial total state that factorizes over the internal and external degrees of freedom of the atoms. Due to the permutational symmetry of the motional state, the cooperative spontaneous emission, governed by a recently derived master equation [F. Damanet et al., Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates γ and γ0 and a single parameter dd describing the dipole-dipole shifts. We solve the dynamics exactly for N = 2 atoms, numerically for up to 30 atoms, and obtain the large-N limit by a mean-field approach. We find that there is a critical difference γ0 − γ that depends on N beyond which superradiance is lost. We show that exact nontrivial dark states (i.e., states other than the ground state with vanishing spontaneous emission) only exist for γ = γ0 and that those states (dark when γ = γ0) are subradiant when γ < γ0. [less ▲]

Detailed reference viewed: 10 (2 ULiège)
See detailMaster equation with quantized atomic motion including dipole-dipole interactions
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

Scientific conference (2016, May 26)

We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion [1]. Our equation provides a unifying ... [more ▼]

We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion [1]. Our equation provides a unifying picture of the consequences of recoil and in- distinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics, and is relevant for experiments with ultracold trapped atoms. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, and we find analytical formulas for a number of relevant states (Gaussian states, Fock states and thermal states). In particular, we show that the dipole-dipole interactions and cooperative photon emission can be modulated through the external state of motion. The effects predicted should be experimen- tally observable with Rydberg atoms [2]. [1] F. Damanet, D. Braun, and J. Martin, arXiv:1512.06676v2. [2] K. Afrousheh, P. Bohlouli-Zanjani, D. Vagale, A. Mugford, M. Fedorov, and J. D. D. Martin, Phys. Rev. Lett. 93, 233001 (2004) [less ▲]

Detailed reference viewed: 24 (8 ULiège)
Full Text
Peer Reviewed
See detailAnticoherence of spin states with point-group symmetries
Baguette, Dorian ULiege; Damanet, François ULiege; Giraud, Olivier et al

Poster (2016, May 18)

Detailed reference viewed: 36 (12 ULiège)
Full Text
Peer Reviewed
See detailChaotic Bohmian trajectories for stationary states
Cesa, Alexandre ULiege; Martin, John ULiege; Struyve, Ward

Poster (2016, May 18)

We study the possibility of chaos for the Bohmian dynamics when the wave function is stationary. Examples of stationary wave functions are given for which there is chaos, as demonstrated by numerical ... [more ▼]

We study the possibility of chaos for the Bohmian dynamics when the wave function is stationary. Examples of stationary wave functions are given for which there is chaos, as demonstrated by numerical computations, for one particle moving in 3 spatial dimensions and for two and three entangled particles in 2 dimensions. What is important for the amount of chaos is the overall complexity of the wave function. Some simple measures that partly capture the complexity of the wave function are considered: the participation ratio and different measures of entanglement. We find that these measures often tend to correlate to the amount of chaos. However, the correlation is not perfect, because the measures do not depend on the intrinsic complexity of the states of a given basis. [less ▲]

Detailed reference viewed: 25 (6 ULiège)
Full Text
Peer Reviewed
See detailSuper- and subradiance from indistinguishable atoms with quantized motion
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

Poster (2016, May 18)

Detailed reference viewed: 19 (4 ULiège)
See detailCollective spontaneous emission with quantized atomic motion
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

Scientific conference (2016, May 09)

Detailed reference viewed: 15 (3 ULiège)
Full Text
Peer Reviewed
See detailScattering theory of walking droplets in the presence of obstacles
Dubertrand, Rémy ULiege; Hubert, Maxime ULiege; Schlagheck, Peter ULiege et al

in New Journal of Physics (2016), 18

We aim to describe a droplet bouncing on a vibrating bath using a simple and highly versatile model inspired from quantum mechanics. Close to the Faraday instability, a long-lived surface wave is created ... [more ▼]

We aim to describe a droplet bouncing on a vibrating bath using a simple and highly versatile model inspired from quantum mechanics. Close to the Faraday instability, a long-lived surface wave is created at each bounce, which serves as a pilot wave for the droplet. This leads to so called walking droplets or walkers. Since the seminal experiment by {\it Couder et al} [Phys. Rev. Lett. {\bf 97}, 154101 (2006)] there have been many attempts to accurately reproduce the experimental results. We propose to describe the trajectories of a walker using a Green function approach. The Green function is related to the Helmholtz equation with Neumann boundary conditions on the obstacle(s) and outgoing boundary conditions at infinity. For a single-slit geometry our model is exactly solvable and reproduces some general features observed experimentally. It stands for a promising candidate to account for the presence of arbitrary boundaries in the walker's dynamics. [less ▲]

Detailed reference viewed: 35 (8 ULiège)
Full Text
See detailMaster equation for collective spontaneous emission with quantized atomic motion
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

Scientific conference (2016, March 02)

We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including the quantization of their motion. Our equation provides a unifying picture of the effects of ... [more ▼]

We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including the quantization of their motion. Our equation provides a unifying picture of the effects of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, generalizing those in Ref. [1]. We find closed-form formulas for a number of relevant states (gaussian states, Fock states and thermal states). In particular, we show that dipole-dipole interactions and cooperative photon emission [2] can be modulated through the external state of motion. As an application of our general formalism, we study the spatial Pauli blocking of two fermionic atoms beyond the Lamb-Dicke regime [3]. [1] G. S. Agarwal, Springer Tracts In Modern Physics 70, 1 (1974). [2] R. H. Dicke, Phys. Rev. 93, 99 (1954). [3] R. M. Sandner, M. Müller, A. J. Daley & P. Zoller, Phys. Rev. A 84, 043825 (2011). [less ▲]

Detailed reference viewed: 20 (6 ULiège)
Full Text
Peer Reviewed
See detailAnticoherence of spin states with point-group symmetries
Baguette, Dorian ULiege; Damanet, François ULiege; Giraud, Olivier et al

Poster (2016, March 02)

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana ... [more ▼]

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana represen- tation of spin states in terms of points on the unit sphere, we analyze the consequences of a point-group symmetry in their arrangement on the quantum properties of the corresponding state [1]. We focus on the identi cation of anticoherent states (for which all reduced density matrices in the symmetric subspace are maximally mixed) associated with point-group-symmetric sets of points. We provide three di erent characterizations of anticoherence and establish a link between point symmetries, anticoherence, and classes of states equivalent through stochastic local operations with classical communication. We then in- vestigate in detail the case of small numbers of qubits and construct in nite families of anticoherent states with point-group symmetry of their Majorana points, showing that anticoherent states do exist to arbitrary order. [1] D. Baguette et al., Phys. Rev. A 92, 052333 (2015). [less ▲]

Detailed reference viewed: 21 (6 ULiège)
Full Text
See detailAnticoherence and entanglement of spin states
Martin, John ULiege; Baguette, Dorian ULiege; Damanet, François ULiege et al

Scientific conference (2016, March 02)

We investigate multiqubit permutation-symmetric states with maxi- mally mixed reduced density matrices in the symmetric subspace [1]. Such states can be viewed as particular spin states, namely anticoher ... [more ▼]

We investigate multiqubit permutation-symmetric states with maxi- mally mixed reduced density matrices in the symmetric subspace [1]. Such states can be viewed as particular spin states, namely anticoher- ent spin states [2]. Using the Majorana representation of spin states in terms of points on the unit sphere [3], we analyze the consequences of degeneracies of the Majorana points and of a point-group symmetry in their arrangement on the existence of anticoherent spin states. We provide different characterizations of anticoherence and establish a link between point symmetries, anticoherence, and SLOCC classes [4]. We consider in detail the case of small numbers of qubits and solve the 4-qubit case completely by identifying and characterizing all 4-qubit anticoherent states. [1] D. Baguette, T. Bastin, and J. Martin, Phys. Rev. A 90, 032314 (2014); O. Giraud et al., Phys. Rev. Lett. 114, 080401 (2015); D. Baguette et al., Phys. Rev. A 92, 052333 (2015). [2] J. Zimba, Electron. J. Theor. Phys. 3, 143 (2006). [3] E. Majorana, Nuovo Cimento 9, 43 (1932). [4] SLOCC classes : Classes of states equivalent through stochastic local operations with classical communication. [less ▲]

Detailed reference viewed: 57 (7 ULiège)
Full Text
Peer Reviewed
See detailMaster equation for collective spontaneous emission with quantized atomic motion
Damanet, François ULiege; Braun, Daniel; Martin, John ULiege

in Physical Review A (2016), 93

We derive a Markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion. Our equation provides a unifying ... [more ▼]

We derive a Markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion. Our equation provides a unifying picture of the consequences of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics, and applies equally well to distinguishable and indistinguishable atoms. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, and we find closed-form formulas for a number of relevant states (Gaussian states, Fock states, and thermal states). In particular, we show that dipole-dipole interactions and cooperative photon emission can be modulated through the external state of motion. [less ▲]

Detailed reference viewed: 19 (6 ULiège)
Full Text
Peer Reviewed
See detailAnticoherence of spin states with point-group symmetries
Baguette, Dorian ULiege; Damanet, François ULiege; Giraud, Olivier et al

in Physical Review A (2015), 92

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana ... [more ▼]

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana representation of spin states in terms of points on the unit sphere, we analyze the consequences of a point-group symmetry in their arrangement on the quantum properties of the corresponding state. We focus on the identification of anticoherent states (for which all reduced density matrices in the symmetric subspace are maximally mixed) associated with point-group-symmetric sets of points. We provide three different characterizations of anticoherence and establish a link between point symmetries, anticoherence, and classes of states equivalent through stochastic local operations with classical communication. We then investigate in detail the case of small numbers of qubits and construct infinite families of anticoherent states with point-group symmetry of their Majorana points, showing that anticoherent states do exist to arbitrary order. [less ▲]

Detailed reference viewed: 31 (5 ULiège)