FY2020 Annual Report

Experimental Quantum Information Physics Unit
Assistant Professor Hiroki Takahashi



The EQuIP unit formally started in April 2020. Hiroki arrived at OIST only in June due to the travel restriction amid the covid-19 pandemic. The only staff member of the unit, Ezra, could only start remotely in the presence of an even stricter travel restriction at the border and his remote working continued until December. Despite this difficult situation we continued putting efforts to get our research going at OIST. Our research activities are categorized as follows: 1) Fabrication of linear ion traps using selective laser etching (SLE) of glass substrates, 2) designing the experimental chamber and peripherals for the ion trap experiment, 3) setting up new labs. 

1. Members


  • Dr. Ezra Kassa, Postdoctoral Scholar (on site from December 2020)

Graduate students

  • Soon Teh (from September 2020)

2. Collaborations

2.1 Fiber-based Fabry-Perot cavities for opto-mecanical NMR

  • Description: This collabration aims to detect nuclear magnetic resonance signals with optical means. The device is an electro-mechanical circuit coupled with a Fabry-Perot optical cavity. Our mission in this collaboration is to provide a miniaturized fiber-based Fabry-Perot cavity optimized for this purpose.
  • Type of collaboration: Joint research
  • Researchers:
    • Professor Koji Usami, University of Tokyo
    • Professor Kazuyuki Takeda, Kyoto University

2.2 Effects of cavity birefringence on remote entanglement generation

  • Description: We studied the impact of birefringence on the cavities we intend to produce and proposed remedies for the adverse impact of imperfections during mirror productions.
  • Type of collaboration: Joint research
  • Researchers:
    • Professor Joseph F. Goldwin, Oxford University

3. Activities and Findings

3.1 Fabrication of linear ion traps

Our main objective in a short term is to combine a linear ion trap with an optical micro-cavity and to successfully couple a single ion to the cavity. For that purpose, a linear Paul trap that accommodates a micro-cavity is indispensable. We designed such a trap, precisely modelled in a 3D CAD, and then tried to actually implement it with SLE. SLE enables us to carve an arbitrary 3D shape out of a silica glass substrate. Such a 3D structure made of glass is subsquently coated with gold to fabricate a set of metal electrodes on its surface. We used the SLE machine (LightFab) and evaporative coating machine (Plassys) available in the nanofab facility at OIST.  It required us a lot of trials and errors on the LightFab and in the etching process until we successfully carved out a desired structure without defects, cracks or overetching.

3.2 Designing the experimental chamber and peripherals for the ion trap experiment

Ion trap experiments happen in ultra-high vacuum envrionment. Therefore in our experiment the ion trap and optical cavity are placed in a vacuum chamber, and necessary laser beams are delivered through vacuum windows. Also in the vacuum chamber, other peripheral components such as nano-positioning stages for the cavity, an electrical routing circuit for rf signals and an atomic oven for loading have to be installed under a proper arrangement with respect to the ion trap. We created a 3D CAD model that includes all the aforementioned components plus vacuum pumps and optics outside the chamber so that we identify and solve potential geometrical conflicts amongst them. After fixing the design we procured necessary components.

3.4 Setting up new labs

Setting up new lab envrionment in Lab4 is ongoing. A construction work to modify the rooms with custom air-conditioning and overhead shelves was done in November. Optical tables were installed subsequently. All the lasers necessary for cooling and trapping Calcium ions were installed in February.  

4. Publications

4.1 Journals

  1. Ryutaro Ohira, Shota Kume, Hiroki Takahashi and Kenji Toyoda
    Polariton blockade in the Jaynes–Cummings–Hubbard model with trapped ions
    Quantum Science and Technology 6, 024015 (2021).
  2. Ryutaro Ohira, Shota Kume, Kyoichi Takayama, Silpa Muralidharan, Hiroki Takahashi and Kenji Toyoda
    Blockade of phonon hopping in trapped ions in the presence of multiple local phonons
    Physical Review A 103, 012612 (2021).
  3. Atsushi Noguchi, Alto Osada, Shumpei Masuda, Shingo Kono, Kentaro Heya, Samuel Piotr Wolski, Hiroki Takahashi, Takanori Sugiyama, Dany Lachance-Quirion and Yasunobu Nakamura
    Fast parametric two-qubit gates with suppressed residual interaction using a parity-violated superconducting qubit
    Physical Review A 102, 062408 (2020).
  4. Costas Christoforou, Corentin Pignot, Ezra Kassa, Hiroki Takahashi and  Matthias Keller
    Enhanced ion–cavity coupling through cavity cooling in the strong coupling regime
    Scientific Reports, 10, 15693 (2020)
  5. Anas R. Peerzada, Callan M. Jobson, Ezra Kassa, Jack Morphew, Xavier Fernandez-Gonzalvo, and  Matthias Keller
    Versatile optical fiber feedthroughs for ultra-high vacuum applications
    Vacuum, 180, 109542 (2020)

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

  1. Takahashi, H. Cavity QED with single ions: Towards photonic interconnects between ion traps (online invited talk), TRiAC workshop, Japan & Germany, Mar. 26 (2021).
  2. Takahashi, H. Strong coupling of a single ion to an optical cavity: Towards photonics interconnects for quantum computers (online invited talk), CECT Meeting, The Institution of Electrical Engineers of Japan, Mar. 23 (2021).
  3. Takahashi, H. Fault-tolerant Quantum Computing with Photonically Interconnected Ion Traps (online invited talk), Moonshot Goal 6 Kick-off Symposium, Japan, Mar. 11 (2021).
  4. Takahashi, H. Strong coupling of a single ion to an optical cavity: Towards photonics interconnects between ion traps (online invited talk), Tohoku Quantum Alliance x OIST, Japan, Jan. 18 (2021).
  5. Takahashi, H. Strong coupling between a single ion and a single photon: Towards photonic interconnects between ion traps (online invited talk), The 41st Annual Meeting of the Laser Society of Japan, Japan, Jan. 18 (2021).
  6. Takahashi, H. Towards photonic interconnects between ion traps for scalable quantum information processing (online contributed talk), CLEO Technical Conference, USA, May 15 (2020).

4.4 Seminars

  1. Takahashi, H. Ion trap quantum computing (online seminar), Spring school of quantum information, Japan, Mar. 26 (2021).
  2. Takahashi, H. Development of quantum technologies in Japan (online seminar), Pacific Forum: 21st Century Technologies, Geopolitics and US-Japan Alliance, Oct. 8 (2020).
  3. Takahashi, H. Strong coupling of a single ion to an optical cavity: Towards quantum photonics interconnects between ion traps (online seminar), Seminar on Precision Physics and Fundamental Symmetries, Jul. 23 (2020).

5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

6. Meetings and Events

6.1 The 3rd Asia-Pacific Workshop for Trapped Quantum Systems (APTQS 2020)

  • Date: Oct. 28-30, 2020
  • Venue: Online
  • 26 speakers.
  • HT as a local co-organizer.

7. Other

Nothing to report.