Quantum simulators based on the global collective light-matter interaction

Physical Review A American Physical Society (2016)

SF Caballero-Benitez, G Mazzucchi, IB Mekhov

We show that coupling ultracold atoms in optical lattices to quantized modes of an optical cavity leads to quantum phases of matter, which at the same time posses properties of systems with both short- and long-range interactions. This opens perspectives for novel quantum simulators of finite-range interacting systems, even though the light-induced interaction is global (i.e. infinitely long range). This is achieved by spatial structuring of the global light-matter coupling at a microscopic scale. Such simulators can directly benefit from the collective enhancement of the global light-matter interaction and constitute an alternative to standard approaches using Rydberg atoms or polar molecules. The system in the steady state of light induces effective many-body interactions that change the landscape of the phase diagram of the typical Bose-Hubbard model. Therefore, the system can support non-trivial superfluid states, bosonic dimer, trimers, etc. states and supersolid phases depending on the choice of the wavelength and pattern of the light with respect to the classical optical lattice potential. We find that by carefully choosing the system parameters one can investigate diverse strongly correlated physics with the same setup, i.e., modifying the geometry of light beams. In particular, we present the interplay between the density and bond (or matter-wave coherence) interactions. We show how to tune the effective interaction length in such a hybrid system with both short-range and global interactions.

Entanglement Renyi alpha entropy

PHYSICAL REVIEW A 93 (2016) ARTN 022324

Y-X Wang, L-Z Mu, V Vedral, H Fan

Pinning of fermionic occupation numbers: General concepts and one spatial dimension

Physical Review A American Physical Society 93 (2016) 042126-

F Tennie, D Ebler, V Vedral, C Schilling

Analytical evidence for the physical relevance of generalized Pauli constraints (GPCs) has recently been provided in Schilling et al. [Phys. Rev. Lett. 110, 040404 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.040404]: Natural occupation numbers λ ≡(λi) of the ground state of a model system in the regime of weak couplings κ of three spinless fermions in one spatial dimension were found extremely close, at a distance Dmin∼κ8 to the boundary of the allowed region. We provide a self-contained and complete study of this quasipinning phenomenon. In particular, we develop tools for its systematic exploration and quantification. We confirm that quasipinning in one dimension occurs also for larger particle numbers and extends to intermediate coupling strengths, but vanishes for very strong couplings. We further explore the nontriviality of our findings by comparing quasipinning by GPCs to potential quasipinning by the less restrictive Pauli exclusion principle constraints. This allows us to eventually confirm the significance of GPCs beyond Pauli's exclusion principle.

Quantum thermodynamics for a model of an expanding Universe


N Liu, J Goold, I Fuentes, V Vedral, K Modi, DE Bruschi

Quantum optical feedback control for creating strong correlations in many-body systems

arXiv (2016)

G Mazzucchi, SF Caballero-Benitez, DA Ivanov, IB Mekhov

Light enables manipulating many-body states of matter, and atoms trapped in optical lattices is a prominent example. However, quantum properties of light are completely neglected in all quantum gas experiments. Extending methods of quantum optics to many-body physics will enable phenomena unobtainable in classical optical setups. We show how using the quantum optical feedback creates strong correlations in bosonic and fermionic systems. It balances two competing processes, originating from different fields: quantum backaction of weak optical measurement and many-body dynamics, resulting in stabilized density waves, antiferromagnetic and NOON states. Our approach is extendable to other systems promising for quantum technologies.

General framework for quantum macroscopicity in terms of coherence

PHYSICAL REVIEW A 93 (2016) ARTN 022122

B Yadin, V Vedral

Converting coherence to quantum correlations

Physical Review Letters American Physical Society 116 (2016) 160407

J Ma, B Yadin, D Girolami, V Vedral, M Gu

Recent results in quantum information theory characterize quantum coherence in the context of resource theories. Here, we study the relation between quantum coherence and quantum discord, a kind of quantum correlation which appears even in nonentangled states. We prove that the creation of quantum discord with multipartite incoherent operations is bounded by the amount of quantum coherence consumed in its subsystems during the process. We show how the interplay between quantum coherence consumption and creation of quantum discord works in the preparation of multipartite quantum correlated states and in the model of deterministic quantum computation with one qubit.

How discord underlies the noise resilience of quantum illumination


C Weedbrook, S Pirandola, J Thompson, V Vedral, M Gu

Power of one qumode for quantum computation

PHYSICAL REVIEW A 93 (2016) ARTN 052304

N Liu, J Thompson, C Weedbrook, S Lloyd, V Vedral, M Gu, K Modi

Collective dynamics of multimode bosonic systems induced by weak quantum measurement

New Journal of Physics IOP Publishing: Open Access Journals (2016)

G Mazzucchi, W Kozlowski, SF Caballero-Benitez, IB Mekhov

In contrast to strong projective measurement, which freezes the system evolution by quantum Zeno effect, weak measurement can effectively compete with standard unitary dynamics leading to nontrivial effects. Here we consider global weak measurement addressing several bosonic modes at the same time, thus preserving quantum superpositions due to the lack of which path information. While for certainty we focus on ultracold atoms, the idea can be generalized to other multimode quantum systems, including various quantum emitters, optomechanical arrays, and purely photonic systems with multiple-path interferometers. We show that light scattering from ultracold bosons in optical lattices can be used for defining macroscopically occupied spatial modes that exhibit long-range coherent dynamics. Even for constant external measurement, the quantum measurement backaction acts on the atomic ensemble quasi-periodically and induces collective oscillatory dynamics of all the atoms. We introduce an effective model for the evolution of the spatial modes and present an analytic solution showing that the quantum jumps drive the system away from its stable point. We confirm our finding describing the atomic observables in terms of stochastic differential equations.

Bond Order via Light-Induced Synthetic Many-body Interactions of Ultracold Atoms in Optical Lattices

arXiv (2016)

SF Caballero-Benitez, IB Mekhov

We show how bond order emerges due to light mediated synthetic interactions in ultracold atoms in optical lattices in an optical cavity. This is a consequence of the competition between both short- and long-range interactions designed by choosing the optical geometry. Light induces effective many-body interactions that modify the landscape of quantum phases supported by the typical Bose-Hubbard model. Using exact diagonalization of small system sizes in one dimension, we present the many-body quantum phases the system can support via the interplay between the density and bond (or matter-wave coherence) interactions. We find numerical evidence to support that dimer phases due to bond order are analogous to valence bond solids.

Macroscopic Quantum Resonators (MAQRO): 2015 update


R Kaltenbaek, M Aspelmeyer, PF Barker, A Bassi, J Bateman, K Bongs, S Bose, C Braxmaier, C Brukner, B Christophe, M Chwalla, P-F Cohadon, AM Cruise, C Curceanu, K Dholakia, L Diosi, K Doeringshoff, W Ertmer, J Gieseler, N Guerlebeck, G Hechenblaikner, A Heidmann, S Herrmann, S Hossenfelder, U Johann, N Kiesel, M Kim, C Laemmerzahl, A Lambrecht, M Mazilu, GJ Milburn, H Mueller, L Novotny, M Paternostro, A Peters, I Pikovski, AP Zanoni, EM Rasel, S Reynaud, CJ Riedel, M Rodrigues, L Rondin, A Roura, WP Schleich, J Schmiedmayer, T Schuldt, KC Schwab, M Tajmar, GM Tino, H Ulbricht, R Ursin, V Vedral

Quantum measurement-induced dynamics of many-body ultracold bosonic and fermionic systems in optical lattices

Physical Review A American Physical Society 93 (2016) 023632

G Mazzucchi, W Kozlowski, SF Caballero-Benitez, TJ Elliott, IB Mekhov

Trapping ultracold atoms in optical lattices enabled numerous breakthroughs uniting several disciplines. Coupling these systems to quantized light leads to a plethora of new phenomena and has opened up a new field of study. Here we introduce a physically novel source of competition in a many-body strongly correlated system: We prove that quantum backaction of global measurement is able to efficiently compete with intrinsic short-range dynamics of an atomic system. The competition becomes possible due to the ability to change the spatial profile of a global measurement at a microscopic scale comparable to the lattice period without the need of single site addressing. In coherence with a general physical concept, where new competitions typically lead to new phenomena, we demonstrate novel nontrivial dynamical effects such as large-scale multimode oscillations, long-range entanglement and correlated tunneling, as well as selective suppression and enhancement of dynamical processes beyond the projective limit of the quantum Zeno effect. We demonstrate both the break-up and protection of strongly interacting fermion pairs by measurement. Such a quantum optical approach introduces into many-body physics novel processes, objects, and methods of quantum engineering, including the design of many-body entangled environments for open systems.

Incoherent quantum feedback control of collective light scattering by Bose-Einstein condensates

arXiv (2016)

DA Ivanov, TY Ivanova, IB Mekhov

It is well known that in the presence of a ring cavity the light scattering from a uniform atomic ensemble can become unstable resulting in the collective atomic recoil lasing. This is the result of a positive feedback due to the cavity. We propose to add an additional electronic feedback loop based on the photodetection of the scattered light. The advantage is a great flexibility in choosing the feedback algorithm, since manipulations with electric signals are very well developed. In this paper we address the application of such a feedback to atoms in the Bose-Einstein condensed state and explore the quantum noise due to the incoherent feedback action. We show that although the feedback based on the photodetection does not change the local stability of the initial uniform distribution with respect to small disturbances, it reduces the region of attraction of the uniform equilibrium. The feedback-induced nonlinearity enables quantum fluctuations to bring the system out of the stability region and cause an exponential growth even if the uniform state is globally stable without the feedback. Using numerical solution of the feedback master equation we show that there is no feedback-induced noise in the quadratures of the excited atomic and light modes. The feedback loop, however, introduces additional noise into the number of quanta of these modes. Importantly, the feedback opens an opportunity to position the modulated BEC inside a cavity as well as tune the phase of scattered light. This can find applications in precision measurements and quantum simulations.

Photonic Maxwell's Demon.

Physical review letters 116 (2016) 050401-

MD Vidrighin, O Dahlsten, M Barbieri, MS Kim, V Vedral, IA Walmsley

We report an experimental realization of Maxwell's demon in a photonic setup. We show that a measurement at the few-photons level followed by a feed-forward operation allows the extraction of work from intense thermal light into an electric circuit. The interpretation of the experiment stimulates the derivation of an equality relating work extraction to information acquired by measurement. We derive a bound using this relation and show that it is in agreement with the experimental results. Our work puts forward photonic systems as a platform for experiments related to information in thermodynamics.

Quantum properties of light scattered from structured many-body phases of ultracold atoms in quantum optical lattices


SF Caballero-Benitez, IB Mekhov

Introducing one-shot work into fluctuation relations


NY Halpern, AJP Garner, OCO Dahlsten, V Vedral

Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light

Atoms MDPI 3 (2015) 392-406

T Elliott, G Mazzucchi, W Kozlowski, SF Caballero-Benitez, I Mekhov

We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyse the entanglement between light and matter and show how it can be exploited for realising multimode macroscopic quantum superpositions, such as Schrödinger cat states, for both bosons and fermions. We provide examples utilising different measurement schemes and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases and significantly altering the phase diagram of the atomic system.

Quantum Optical Lattices for Emergent Many-Body Phases of Ultracold Atoms.

Physical review letters 115 (2015) 243604-

SF Caballero-Benitez, IB Mekhov

Confining ultracold gases in cavities creates a paradigm of quantum trapping potentials. We show that this allows us to bridge models with global collective and short-range interactions as novel quantum phases possess properties of both. Some phases appear solely due to quantum light-matter correlations. Because of a global, but spatially structured, interaction, the competition between quantum matter and light waves leads to multimode structures even in single-mode cavities, including delocalized dimers of matter-field coherences (bonds), beyond density orders as supersolids and density waves.

Quantum macroscopicity versus distillation of macroscopic superpositions

PHYSICAL REVIEW A 92 (2015) ARTN 022356

B Yadin, V Vedral