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June 2017: Spectral signatures of many-body localization of interacting photons (collaboration with Google-Martinis group)

Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions between particles facilitate thermalization, but, can interacting systems always equilibrate regardless of parameter values? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases.  However, most experimental techniques only indirectly probe the many-body energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy levels of interacting photons. We benchmark this method by capturing the intricate energy spectrum predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By increasing disorder, the spatial extent of energy eigenstates at the edge of the energy band shrink, suggesting the formation of a mobility edge. At strong disorder, the energy levels cease to repel one another and their statistics approaches a Poisson distribution -the hallmark of transition from the thermal to the many-body localized phase. Our work introduces a new many-body spectroscopy technique to study quantum phases of matter.

P. Roushan, C. Neill, J. Tangpanitanon, V.M. Bastidas, A. Megrant, R. Barends, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, A. Fowler, B. Foxen, E. Je rey, J. Kelly, E. Lucero, J. Mutus, M. Neeley, C. Quintana, D. Sank, A. Vainsencher, J. Wenner, T. White, H. Neven, D. G. Angelakis, and J. Martinis [under review]

Pre-Print: https://arxiv.org/abs/1709.07108

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May 2017: Quantum Simulators with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics

Check our book on “Quantum Simulators with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics” by Springer!

This book reviews progress towards quantum simulators based on photonic and hybrid light-matter systems, covering theoretical proposals and recent experimental work.  Quantum simulators are specially designed quantum computers. Their main aim is to simulate and understand complex and inaccessible quantum many-body phenomena found or predicted in condensed matter physics, materials science and exotic quantum

 

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May 2017: A diagrammatic Diagrammatic Approach to Multiphoton Scattering

Authors

T.F. See, C. Noh, D.G. Angelakis, “A diagrammatic Diagrammatic Approach to Multiphoton Scattering”, Phys. Rev. A 95, 053845 (2017)

Abstract

We present a method to systematically study multiphoton transmission in one-dimensional systems comprised of correlated quantum emitters coupled to input and output waveguides. Within the Green’s function approach of the scattering matrix (S matrix), we develop a diagrammatic technique to analytically obtain the system’s scattering amplitudes while at the same time visualize all the possible absorption and emission processes. Our method helps to reduce the significant effort in finding the general response of a many-body bosonic system, particularly the nonlinear response embedded in the Green’s functions. We demonstrate our proposal through physically relevant examples involving scattering of multiphoton states from two-level emitters as well as from arrays of correlated Kerr nonlinear resonators in the Bose-Hubbard model.

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November 2016: Topological pumping of photons in nonlinear resonator arrays

” The inspiration for a new scheme to transport interacting quantum particles has its roots in Ancience Greece. In Thouless pumping, transport happens because of the topology of fields acting on the quantum particles – similar to the way that an Archimedes’ screw pump can move water up a hill,.. ”
Read more from CQT highlight for non specialists ” Topological scheme for transporting quantum particles inspired by Nobel winner’s work “

This work is also highlighted in 7 science news including EurekaAlert!, Phys.org, Health Medicinet, Nanowerk, Nanotechnology Now, Sky Nightly, and Space Daily.

Authors

J. Tangpatinanon, V. M. Bastidas, P. Roushan, S. Assam, D. Jaksch, D. G. Angelakis, “Topological pumping with photons in nonlinear resonator arrays”, Physical Review Letters, 117,  213603 (2016)

Abstract

We show how to implement topological or Thouless pumping of interacting photons in one-dimensional nonlinear resonator arrays by simply modulating the frequency of the resonators periodically in space and time. The interplay between the interactions and the adiabatic modulations enables robust transport of Fock states with few photons per site. We analyze the transport mechanism via an effective analytic model and study its topological properties and its protection to noise. We conclude by a detailed study of an implementation with existing circuit-QED architectures.

Image credit: Embed from Getty Images

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April 2016: Review on “Quantum Simulations and Many-Body Physics with Light”

Our comprehensive review on “Quantum Simulations and Many-Body Physics with Light” is out at  Reports in Progress in Physics 80, 016401 (2016).

In this review we discuss the works in the area of quantum simulation and many-body physics with light, from the early proposals on equilibrium models to the more recent works in driven dissipative platforms.. We review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, photonic crystals and nanophotonic fibers interfaced with cold atoms.

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November 2015: Few Photon Transport in Many-Body Photonic Systems: A Scattering Approach

With the help of two-photon scattering matrix of in- and out-states, we find that the use of quantum input states in photonic quantum simulators such as those implemented in coupled cavity arrays, allows one to observe not only stronger spectroscopic signals of the underlying strongly correlated states but also a faithful representation of their intensity-intensity correlations, as compared to the conventional classical driving fields. Our analysis can be applied for many-body spectroscopy of any many-body model amenable to a photonic quantum simulation,  including the Jaynes-Cummings-Hubbard, the extended Bose-Hubbard, and a whole range of spin models.

Authors

C. Lee, C. Noh, N. Schetakis,  D. G. Angelakis “Few photon transport in nonlinear cavity arrays:Probing signatures of strongly correlated states”, Phys. Rev. A 92, 063817 (2015).

Abstracts

We study the quantum transport of multiphoton Fock states in one-dimensional Bose-Hubbard lattices implemented in QED cavity arrays (QCAs). We propose an optical scheme to probe the underlying many-body states of the system by analyzing the properties of the transmitted light using scattering theory. To this end, we employ the Lippmann-Schwinger formalism within which an analytical form of the scattering matrix can be found. The latter is evaluated explicitly for the two-particle, two-site case which we use to study the resonance properties of two-photon scattering, as well as the scattering probabilities and the second-order intensity correlations of the transmitted light. The results indicate that the underlying structure of the many-body states of the model in question can be directly inferred from the physical properties of the transported photons in its QCA realization. We find that a fully resonant two-photon scattering scenario allows a faithful characterization of the underlying many-body states, unlike in the coherent driving scenario usually employed in quantum master-equation treatments. The effects of losses in the cavities, as well as the incoming photons’ pulse shapes and initial correlations, are studied and analyzed. Our method is general and can be applied to probe the structure of any many-body bosonic model amenable to a QCA implementation, including the Jaynes-Cummings-Hubbard model, the extended Bose-Hubbard model, as well as a whole range of spin models.

 

 

 

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April 2015: Optical simulation of charge conservation violation and Majorana dynamics

“Forbidden physics has been seen in an experiment – sort of. CQT researchers and collaborators in Germany, Austria and India simulated with light the behaviour of an impossible particle known as a Majoranon…”
Read more from CQT highlight for non specialists, ” Light mimics forbidden particle “

This work was chosen for a focus article in Οptics & Photonics News (OPN)  “Using light to simulate unphysical particles”. ! It has also appeared in the Science Section, International Business Times, as well as phys.org  and sciencedaily

Authors

R. Keil, C. Noh, A. Rai, S. Stutzer, S. Nolte, D. G. Angelakis, A. Szameit “Experimental simulation of charge conservation violation and Majorana dynamics”, Optica 2,454 (2015)

Abstracts

Unphysical solutions are ruled out in physical equations, as they lead to behavior that violates fundamental physical laws. One of the celebrated equations that allows unphysical solutions is the relativistic Majorana equation, thought to describe neutrinos and other exotic particles predicted in theories beyond the standard model. The neutrally charged Majorana fermion is the equation’s physical solution, whereas the charged version is, due to charge nonconservation, unphysical and cannot exist. Here, we present an experimental scheme simulating the dynamics of a charged Majorana particle by light propagation in a tailored waveguide chip. Specifically, we simulate the free-particle evolution as well as the unphysical operation of charge conjugation. We do this by exploiting the fact that the wave function is not a directly observable physical quantity and by decomposing the unphysical solution to observable entities. Our results illustrate the potential of investigating theories beyond the standard model in a compact laboratory setting.