PD fellowship of the JSPS on the project :Development of Novel Light–Matter Coupled Systems in the Ultrastrong Coupling Regime Using Semiconductor Nanostructures

LIMMS/CNRS-IIS IRL 2820 (Laboratory for Integrated Micro Mechatronic Systems) is an international laboratory between the French CNRS (Centre National de la Recherche Scientifique) and Institute of Industrial Science (IIS), The University of Tokyo, located in Komaba, Tokyo. Since its creation in 1995, LIMMS has welcomed more than 380 researchers from France and Europe.

LIMMS opens a new postdoctoral position in the laboratory of Associate Professor (Kazuyuki KUROYAMA, web: https://www.qnel.iis.u-tokyo.ac.jp/en/), Institute of Industrial Science, the University of Tokyo.

Responsibilities:

The PI’s group at IIS, UTokyo investigates integrated platforms that combine semiconductor quantum nanostructures with terahertz (THz) resonators to realize and control novel light–matter coupled systems. In cavity quantum electrodynamics with extremely small mode volumes and collective excitations, the interaction can reach the ultrastrong coupling regime, where the coupling strength becomes comparable to the bare photon energy. In this unconventional regime, virtual light–matter excitations can emerge even in the absence of external driving and are expected to enable novel phenomena and exotic condensed-matter phases (“cavity quantum materials”), as well as new functionalities for quantum information technologies. However, experimental demonstrations remain limited, and further exploration is highly desired.

To observe phenomena induced by virtual excitations, it is crucial to enhance and control vacuum-dressed light–matter interactions, for example by implementing time-dependent modulation of the coupling strength and by engineering coupled-cavity (resonator-array) systems. We have recently demonstrated an electrically tunable light–matter system based on GaAs heterostructure nanodevices—such as a quantum point contact and a quantum dot—integrated with THz resonators, and observed light–matter coupling via photocurrent measurements under THz irradiation. In addition, we have demonstrated ultrastrong coupling in near-field–coupled THz resonators. We are now aiming to leverage these experimental achievements toward the observation of virtual-excitation–induced phenomena.

In this project, we aim to (i) elucidate the physical mechanism that enables electrical control of the coupling strength in integrated nanodevice–THz resonator systems, and (ii) develop and optimize ultrastrong light–matter coupling in near-field–coupled resonator arrays. Together, these technologies will provide a new avenue toward cavity quantum materials. Furthermore, resonator arrays may enable long-range quantum state transfer mediated by THz cavity modes. The recruited postdoctoral researcher is expected to join and pursue this project. Key tasks include:

• Design, fabrication, and characterization of THz antenna/resonator–nanostructure integrated devices on GaAs-based heterostructure wafers (cleanroom lithography, metallization, etching, and packaging).
• Low-temperature electrical and THz measurements (transport and photocurrent spectroscopy), including development of experimental protocols for electrical control of the coupling.
• Data analysis and quantitative evaluation of coupling strength/tunability versus structural parameters, in collaboration with theory/analysis partners.
• Dissemination of results through papers and conference presentations; contribution to collaborative research with IIS semiconductor groups and a CNRS laboratory.

The laboratory is well equipped with nanofabrication facilities and low-temperature THz measurement setups.

Fellowship periods and periods for arrival in Japan: Two years starting between September 1^st and November 30, 2026

Rewards: Paid equivalent to the JSPS Post-Doctoral position

1. Airfare: A round-trip air ticket (based on JSPS’s regulations)

2. Maintenance Allowance: 362,000 JPY per month

3. Miscellaneous: A setting-in allowance of 200,000 JPY, Overseas travel insurance, etc.

Skills:

Candidates are expected to have a background of solid states physics and/or device physics and have interests in nanotechnologies/nano-sciences. Skills on nanofabrication using lithography technique and small signal measurements will be helpful. A challenging spirit would help a lot for tackling this interdisciplinary and cutting-edge research area.

Goals:

The postdoctoral researcher is expected to develop a strong working knowledge of ultrastrong light–matter coupling and to acquire the experimental skills required for this project, including device fabrication and low-temperature electrical/terahertz characterization. The researcher will then perform a systematic study of how coupling strength and electrical tunability depend on device and resonator design parameters, with the goal of optimizing the integrated architectures. The researcher will also help realize and enhance ultrastrong coupling in near-field–coupled THz resonators and resonator arrays. These developments will enable exploration of quantum phase transitions in the ultrastrong coupling regime and may open pathways toward new functionalities for quantum information technologies.