## Upcoming Events

April 28th (Tuesday) from 2:00 p.m.

Main Research Building, room 535-537 (5th floor Seminar room)

Dr. Roberto Stassi (Dipartimento di Fisica e Chimica, Group of Interdisciplinary Theoretical Physics, Università di Palermo and CNISM, Italy)

Quantum vacuum radiation in ultrastrong coupling cavity QED and in stripline waveguides

The dynamical Casimir effect predicts that, when a mirror is shaken into empty space, it emits light. Such a surprising prediction has been confirmed experimentally only recently, when photons emitted out of the vacuum have been observed in a superconducting waveguide [1,2]. Interestingly, the dynamical Casimir effect emits photons in entangled pairs. In this presentation I show how, going beyond the single waveguide paradigm using a scalable array, it is possible to create multipartite nonclassical states, with the possibility to control the long-range quantum correlations of the emitted photons. In particular, our finite-temperature theory shows how maximally entangled NOON states can be engineered in a realistic setup. Moreover, I show that a spontaneous release of virtual photon pairs can occur in a quantum optical system in the ultrastrong coupling regime. In this regime, which is attracting interest both in semiconductor and superconducting systems, the light-matter coupling rate becomes comparable to the bare resonance frequency of photons. In contrast to the dynamical Casimir effect and other pair creation mechanisms, this phenomenon does not require external forces or time dependent parameters in the Hamiltonian [3,4].

[1] J. R. Johansson, G. Johansson, C. M. Wilson and Franco Nori, Dynamical Casimir Effect in a Superconducting Coplanar Waveguide, Phys. Rev. Lett. 103, 147003 (2009), DOI: 10.1103/PhysRevLett.103.147003.

[2] C. M. Wilson, G. Johansson, A. Pourkabirian, M. Simoen, J. R. Johansson, T. Duty, F. Nori & P. Delsing, Observation of the dynamical Casimir effect in a superconducting circuit, Nature 479, 376 (2011), DOI: 10.1038/nature10561.

[3] R. Stassi, A. Ridolfo, O. Di Stefano, M. J. Hartmann, and S. Savasta, Spontaneous Conversion from Virtual to Real Photons in the Ultrastrong-Coupling Regime, Phys. Rev. Lett. 110, 243601 (2013), DOI: 10.1103/PhysRevLett. 110.243601.

[4] L. Garziano, A. Ridolfo, R. Stassi, O. Di Stefano, and S. Savasta, Switching on and off of ultrastrong light-matter interaction: Photon statistics of quantum vacuum radiation, Phys. Rev. A 88, 063829 (2013), DOI: 10.1103/PhysRevA

April 30th (Thursday) from 2:00 p.m.

Main Research Building, room 535-537 (5th floor Seminar room)

Mr. Luigi Garziano (Dipartimento Fisica e Scienze della Terra, Messina University, ITALY)

Exploring the USC regime in circuit QED and cavity optomechanics

Recently, due to the experimental progress in the development of circuit QED systems, it is possible to obtain the so called ultra-strong coupling (USC) regime between one or more artificial atoms (qubits) and a superconducting resonator. The USC regime presents indeed a great variety of phenomena that cannot be observed in the conventional weak- and strong-coupling regimes [1,2]. For example, situations may arise where the resonator field acquires a nonzero expectation value in the system ground state. It is possible to demonstrate that, in this case, the parity symmetry of an additional artificial atom with an even potential is broken by the interaction with the resonator [3]. Such a mechanism shares some analogies with the Higgs mechanism where the gauge symmetry of the weak force’s gauge bosons is broken by the nonzero vacuum expectation value of the Higgs field. These results can open the way to controllable experiments on symmetry-breaking mechanisms induced by nonzero vacuum expectation values.

Cavity-optomechanics experiments are also rapidly approaching the USC (or single-photon) regime, where the radiation pressure of a single photon displaces the mechanical resonator by more than its zero-point uncertainty. Ultrastrong interactions in optomechanical systems can be used to force the system ground state to evolve into an arbitrary quantum state of mechanical motion in a completely controlled and deterministic manner. The general strategy for creating such states was first described by Law and Eberly in the context of cavity QED [4] and has been applied to optomechanical systems for the synthesis of arbitrary nonclassical motional states [5] and for engineering arbitrary motional and entangled states of a single trapped ion beyond the Lamb-Dicke limit [6]. In contrast to the Law and Eberly algorithm, a new protocol has been recently proposed in order to synthsesize an arbitrary superposition of N Fock states by applying in single-step N classical optical signals of different frequencies for a common time interval [7]. Since a key requirement for synthesizing arbitrary quantum states is that the preparation time needs to be much shorter than the decoherence time, the proposed scheme provides a promising strategy to fully control the quantum state of massive mechanical oscillators. This scheme can be applied to various strongly interacting quantum systems as trapped ions beyond the Lamb-Dicke regime and cavity QED into the ultrastrong coupling regime. The protocol can also be extended for the generation of entangled states between different mechanical oscillators.

[1] A Ridolfo et al, “Photon blockade in the ultrastrong coupling regime” Phys. Rev. Lett. 109, 193602 (2013)

[2] R Stassi et al, “Spontaneous conversion from virtual to real photons in the ultrastrong-coupling regime”, Phys. Rev. Lett. 110, 243601 (2013)

[3] L Garziano et al, “Vacuum-induced symmetry breaking in a superconducting quantum circuit” , Phys. Rev. A 90, 043817 (2014)

[4] C. K. Law and J. H. Eberly, “Arbitrary Control of a Quantum Electromagnetic Field”, Phys. Rev. Lett. 76, 1055 (1996)

[5] X.-W. Xu, H. Wang, J. Zhang, and Y. X. Liu, “Engineering of nonclassical motional states in optomechanical systems”, Phys. Rev. A 88,063819 (2013)

[6] L. F.Wei,Y.-x. Liu, and F. Nori, “Engineering quantum pure states of a trapped cold ion beyond the Lamb-Dicke limit”, Phys. Rev. A 70, 063801 (2004)

[7] L Garziano et al, “Single-step arbitrary control of mechanical quantum states in ultrastrong optomechanics”, Phys. Rev. A 91, 043817 (2015)

May 7th (Thursday) from 1:30 p.m.

Dr. Erik Gauger (Institute of Photonics and Quantum Sciences, Heriot-Watt University, UK)

Superabsorption, dark-state protection and optical ratchets: Harnessing collective effects for enhanced light absorption with coupled nanostructures

Main Research Building, room 435-437 (4th floor Seminar room)

I will discuss ring-like structures of optically active quantum nanostructures which interact with a common electromagnetic environment as well as experiencing the influence of their condensed matter host environment. Often considered detrimental, I will argue that the fundamentally present pairwise couplings of such systems can in fact be an asset for unlocking light absorption beyond what is possible classically. Suitably engineered systems may support one or more of several distinct effects contributing to quantum enhanced photon absorption: inverting superradiance, breaking detailed balance, und optical ratcheting. Potential practical applications of these effects include improved photon detectors and light harvesting devices.

1) Nature Communications 5, Article number: 4705 doi:10.1038/ncomms5705 (2014). http://www.nature.com/ncomms/2014/140822/ncomms5705/full/ncomms5705.html .

2) http://arxiv.org/abs/1504.05849

http://home.eps.hw.ac.uk/~eg7/

The seminar on 8th May (Fri.)

Guillaume Lambard (Research Fellow, Institute for Basic Science Daejeon, Republic of Korea)

A novel direct method to the surface density of dark matter in spirals

Main Research Building, Room 433

15:30-16:30

May 12 (Tues) 13:30-16:00

The 5th iTHES Academic-Industrial Lecture:

"Artificial Intelligence : Present and Future"

(Note that the schedule has been changed from the last announcement)

schedule:

13:30-14:30 Yutaka Matsuo (Univ. Tokyo) Deep learning: present and future

http://ymatsuo.com/index.html

14:30-15:00 Break

15:00-16:00 Koichi Takahashi (QBiC) AI and Science/Technology

http://www.riken.jp/en/research/labs/qbic/comput_biol/biochem_sim/

Place: Okochi Hall

The seminar on 15th May (Fri.)

Shin'ichiro Ando (Assistant Professor, GRAPPA Institute at University of Amsterdam)

Cosmic gamma-ray and neutrino backgrounds: Astrophysical and dark matter implications

Main Research Building, Room 224-226

14:00-15:00

Prof.Yasuhiro Masuda (Institute of Particle and Nuclear Studies, KEK)

EDM Measurement with Ultracold Neutrons

Fri 29th May 2015 11:00-12:00

Main research building, 5th floor, 535,537

CP violation is one of important issues in particle physics. The CP violation induces an electric dipole moment in the neutron (nEDM). With nEDM, many theories of particle physics have been tested. Although the standard model predicts very small values of nEDM, new physics such as supersymmetric theory as well as multi-Higgs model, which is beyond the standard model, predicts nEDM values in a 10^{-27} e cm region. The present state of the arts nEDM measurement is at Grenoble, which shows the upper limit of 3×10^{-26} e cm. In this measurement, ultracold neutrons (UCN) was used. UCN are very low energy neutrons, which can be confined in a measurement cell. The precision of the measurement was limited by the number of UCN in the cell, but the improvement of the number of UCN was strongly limited by Liouville’s theorem. Many institutes have been developing super thermal UCN sources, which get rid of this limitation. Here, we discuss our approach to this problem. Our UCN source became world competitive. We also discuss the present status and the future direction of our nEDM measurement.

Kazunori Kohri (KEK)

Close Encounters of the Dark Matter

12:30-13:30, May 29.

Room 535-537 in the Main Research Build.

I review the current status of the dark matter research for non-specialists.

June 4 (Thur.) from 2:00 pm

Dr. William Witczak-Krempa (https://www.perimeterinstitute.ca/people/william-witczak-krempa )

Constraining quantum critical dynamics: 2+1D Ising model & beyond

Rm 154&156, Main Research Building, Wako campus, RIKEN

Quantum critical (QC) phase transitions generally lead to the destruction of quasiparticles. The resulting correlated quantum fluid, when thermally excited, displays rich universal dynamics. We establish non-perturbative constraints on the linear-response dynamics of QC systems at finite temperature, in spatial dimensions above one. Specifically, we analyze the large frequency/momentum asymptotics of observables, which we use to derive powerful sum rules. The general results are applied to the O(N) Wilson-Fisher fixed point (CFT), describing the QC Ising and XY models when N=1,2, respectively. We'll contrast the results with Dirac fermions. Our focus will be on the order parameter susceptibility, conductivity, and shear viscosity. Connections to quantum Monte Carlo simulations, experiments and AdS/CFT will be made.

It's based on my recent paper (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.177201 ), and other works with Subir Sachdev.

Dr. Tomoyuki Higuchi

(The Institute of Statistical Mathematics)

"Interaction, Integration, and Design: Key elements for success on promoting the interdisciplinary research"

(in Japanese)

June 4 (Thur.) 2015, 10：30－11：30

Main research building 435-437

2nd String Theory in Greater Tokyo

http://indico.ipmu.jp/indico/conferenceDisplay.py?ovw=True&confId=68

June 9th, 2015, 9:30-16:20

RIKEN, Nishina Hall

================================

We invite the following two speakers:

================================

Michele Del Zotto(Harvard Univ)

Masaki Shigemori(Kyoto Univ)

================================

They will give pedagogical talks about forefront of sting theory.

We also have local and short talk speakers:

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Akinori Tanaka (RIKEN)

Tetsuji Kimura (Tokyo Institute of Technology)

Tomoki Nosaka (Kyoto University)

Hironori Mori (Osaka University)

Yoshiki Sato (Kyoto University)

Hiroyuki Shimizu (Tokyo University)

Shotaro Shiba (Kyoto Sangyo University)

Sotaro Sugishita (Kyoto University)

================================

Koji Hashimoto (Osaka Univ.)

"How to see internal space"

June 12 (Fri) 11:00-

Main Research bldg. 248

Is internal space a space?

Internal space, namely, the field space on which some global symmetry (such as U(1) group) acts, is called "internal space" but I don't know precisely why it is called so. In this talk I will explore the question and will come to a certain conclusion, using our new result on general effective action of internal moduli space of domain walls.

"Symposium on the Present and Future of iTHES" originally planned on June 15 (Mon), 2015

is postponed until Fall or Winter of this year from various constraints. We will announce the new date as soon as decided. Thanks for your understanding.

Tetsuo Hatsuda

**iTHES Colloquium**

July 6 (Mon) 15:30-

"Thermodynamics of Information Processing"

Prof. Takahiro Sagawa

(Dept. of Applied Phys., Univ. of Tokyo)

http://noneq.c.u-tokyo.ac.jp/index_e.html

place: Nishina Hall

(Building 13, E-4 area in the following map)

http://www.riken.jp/~/media/riken/access/wako-map/map2_p_150105.pdf

abstract:

In this decade, thermodynamics of information has attracted renewed attentions in light of modern nonequilibrium statistical mechanics, leading to a new field of "information thermodynamics." This topic is related to the foundation of the second law of thermodynamics, which dates back to the thought experiment of "Maxwell's demon" in the nineteenth century. In this talk, I will review the recent progress in information thermodynamics, in both terms of theory and experiment. Theoretically, I will focus on the generalization of the second law of thermodynamics to information processing, where information contents and thermodynamic variables are treated on an equal footing. I will also talk about our experimental realization of Maxwell's demon with a single electron. Moreover, I will talk about our recent result on an application of information thermodynamics to biological signal transduction of E. Coli chemotaxis.

Seminar

"Hypernuclear Spectra within Mean Field and Beyond Mean Field Approach"

Dr. Peter Vesely, a specialist of hypernucleus.

Date and time: July 27, 14:00

Place: room 224 of the main research building

For detail, please see

http://snp.riken.jp/seminar.html

## Event report

ECT* (Eurpean Centre for Theoretical Studies in Nuclear Physics and Related Areas) http://www.ectstar.eu/

ECT* is located in Trento, Italy and is sponsored by Bruno Kessler Foundation (FBK) http://www.fbk.eu/ as well as by EU Member countries. It provides various scientific activities (workshops, schools, doctoral training programs etc) in nuclear physics, astrophysics, particles physics, and condensed matter physics.

Currently, a doctoral training program "Computational Nuclear Physics - Hadrons, Nuclei and Dense Matter" (April 13 - May 22) is being held. I (Tetsuo Hatsuda) went to ECT* to give 10 hours blackboard lectures last week (April 20-24). http://www.ectstar.eu/node/1286 . Graduate students from all over the world (India, Turkey, Lebanon, South Africa, Japan, Italy, England, Ireland, France, Germany, Czech) are attending this 6 weeks program. In the morning, there are 2-hour lecture (1+1 with a coffee break). After taking a good lunch together at a local Italian restaurant, there are discussions sessions and/or student presentations in the afternoon. Students are living together in the nearby accommodation, so that they can interact with each other even at night.

Good location of ECT* (see the photo "Villa Tambosi" which is 15 min. bus drive from the city center to the mountain side) and the international atmosphere with good lectures and good foods attract many talented graduate students to this program every year. Although it was tough for me to lecture for more than 10 hours in 5 days, I enjoyed good questions from the students very much. Note that Trento is an old and beautiful city located in northern part of Italy, http://en.wikipedia.org/wiki/Trento .

Ciao !

## Person of the week

Taro Kimura

"Linking loops in ABJM and refined theory"

http://arxiv.org/abs/1503.01462

A goal of knot theory is to give an efficient way to characterize the shape of a knot. Physicists try to solve this problem using (topological) quantum field theory, by identifying a knot as a particle trajectory. We consider this kind of loop amplitude in a new theory, called ABJM theory, which was originally introduced in the context of string theory and M-theory. We show that this loop amplitude is reduced to a (super)matrix integral by the localization method, and compute the two- and three-link amplitudes. We obtain a factorization of the link amplitude and the Verlinde formula in a sector of supergroup representations. We also propose a refined version of ABJM theory, and compute some refined link amplitudes.