Local reversibility and entanglement structure of many-body ground states


T Kuwahara, I Arad, L Amico, V Vedral

Quantum State Reduction by Matter-Phase-Related Measurements in Optical Lattices

arXiv (2016)

W Kozlowski, SF Caballero-Benitez, IB Mekhov

A many-body atomic system coupled to quantized light is subject to weak measurement. Instead of coupling light to the on-site density, we consider the quantum backaction due to the measurement of matter-phase-related variables such as global phase coherence. We show how this unconventional approach opens up new opportunities to affect system evolution and demonstrate how this can lead to a new class of measurement projections, thus extending the measurement postulate for the case of strong competition with the system's own evolution.

A Nanophotonic Structure Containing Living Photosynthetic Bacteria.

Small (Weinheim an der Bergstrasse, Germany) 13 (2017)

D Coles, LC Flatten, T Sydney, E Hounslow, SK Saikin, A Aspuru-Guzik, V Vedral, JK-H Tang, RA Taylor, JM Smith, DG Lidzey

Photosynthetic organisms rely on a series of self-assembled nanostructures with tuned electronic energy levels in order to transport energy from where it is collected by photon absorption, to reaction centers where the energy is used to drive chemical reactions. In the photosynthetic bacteria Chlorobaculum tepidum, a member of the green sulfur bacteria family, light is absorbed by large antenna complexes called chlorosomes to create an exciton. The exciton is transferred to a protein baseplate attached to the chlorosome, before migrating through the Fenna-Matthews-Olson complex to the reaction center. Here, it is shown that by placing living Chlorobaculum tepidum bacteria within a photonic microcavity, the strong exciton-photon coupling regime between a confined cavity mode and exciton states of the chlorosome can be accessed, whereby a coherent exchange of energy between the bacteria and cavity mode results in the formation of polariton states. The polaritons have energy distinct from that of the exciton which can be tuned by modifying the energy of the optical modes of the microcavity. It is believed that this is the first demonstration of the modification of energy levels within living biological systems using a photonic structure.

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 93 (2016) ARTN 042126

F Tennie, D Ebler, V Vedral, C Schilling

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

Quantum Processes Which Do Not Use Coherence

PHYSICAL REVIEW X 6 (2016) ARTN 041028

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

Converting Coherence to Quantum Correlations.

Physical review letters 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.

Engineering Many-Body Dynamics with Quantum Light Potentials and Measurements

Phys. Rev. A APS 94 (2016) 013614

TJ Elliott, IB Mekhov

Interactions between many-body atomic systems in optical lattices and light in cavities induce long-range and correlated atomic dynamics beyond the standard Bose-Hubbard model, due to the global nature of the light modes. We characterize these processes, and show that uniting such phenomena with dynamical constraints enforced by the backaction resultant from strong light measurement leads to a synergy that enables the atomic dynamics to be tailored, based on the particular optical geometry, exploiting the additional structure imparted by the quantum light field. This leads to a range of tunable effects such as long-range density-density interactions, perfectly correlated atomic tunneling, superexchange, and effective pair processes. We further show that this provides a framework for enhancing quantum simulations to include such long-range and correlated processes, including reservoir models and dynamical global gauge fields.

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 93 (2016) ARTN 023632

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

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.

Pinning of fermionic occupation numbers: Higher spatial dimensions and spin

PHYSICAL REVIEW A 94 (2016) ARTN 012120

F Tennie, V Vedral, C Schilling