QSE Quantum Seminar - Novel Pockels materials beyond Lithium niobate and barium titanate for quantum electro-optical applications & Hybrid Technologies with high-performance superconducting circuits

Please join us for the QSE Center Quantum Seminar with Christian Haffner from IMEC, who will give the talk "Novel Pockels materials beyond Lithium niobate and barium titanate for quantum electro-optical applications" and Atsushi Noguchi from University of Tokyo, who will give the talk "Hybrid Technologies with high-performance superconducting circuits" on Wednesday February 26^th. 
Location: BS 270.

Pizzas will be available before the seminar at 12:00. All PhDs, postdocs, students, and PIs are welcome to join us.

TITLE: Novel Pockels materials beyond Lithium niobate and barium titanate for quantum electro-optical applications & Hybrid Technologies with high-performance superconducting circuits

ABSTRACT:

1. Quantum computers face many challenges towards upscaling the number of qubits and increasing their computational power. For superconducting qubits, this is the radio frequency (RF) -bottleneck between the qubit processor inside the cryostat and the room temperature control and readout electronics. And like for their classical counterparts, hope lies in replacing the RF-links by optical fibers, resulting in a hybrid situation where RF-qubits will be used for computation and optical qubits will serve for remote communication. However, electro-optical (EO) transducers that parametrically amplify RF-qubits directly to optical qubits with a unity efficiency have thus far remained elusive. Key to a unity efficiency are materials that feature low losses, strong nonlinearities and that allow to squeeze down the electro-magnetic field to smallest volumes. Current research focuses on devices based on opto-electro-mechanics or on lithium niobate devices - the classical workhorse of long-range optical communication. In this talk, we discuss high-k strontium titanate as a potential new material that could provide nonlinearities larger than lithium niobate, its unique challenges for EO-transduction and our progress on thin-film integration.
2. Quantum information science has evolved with the discovery and proposal of promising applications and is now entering the phase of testing them using actual quantum hardware. However, currently available quantum systems are still vulnerable to environmental noise and energy loss. Hence, implementing quantum error correction [1] in a scalable approach is essential to demonstrate their potential and real-time error corrections beyond break-even have been recently demonstrated with superconducting quantum circuits [2,3]. There is still a huge overhead toward large-scale fault tolerance quantum computing, which can be suppressed by achieving ultra-small-error quantum manipulation [4]. In addition to the advancements in quantum information science through superconducting qubits, the performance of superconducting circuits has improved by several orders of magnitude over decades. These superconducting technologies are not only applicable to superconducting qubits but also to other types of quantum hardware, contributing to the reduction of error rates. 
     We investigated the high Q microwave resonator using epitaxial grown TiN film on silicon substrates [5]. Our two-dimensional microwave resonator reaches a quality factor of 10 million at the single photon level and 100 million at the high-power input, which is limited by the surface loss of the interface between the material. We also develop high Q membrane oscillators with the highly-stressed epitaxial TiN film, which can be an ultra-long life quantum memory of the superconducting qubit. We evaluated its quality factor as ~10 million with an optical interferometer at 2 K. These technologies increase not only the performance of the superconducting qubit, but also other quantum systems like ion traps. Ion trap quantum system is another promising candidate of the quantum system for quantum information processing. The ultra-precise quantum manipulations have been achieved with trapped ions and especially a fidelity of 99.97% has been reported for a microwave-based two-qubit gate [6] by the strong magnetic RF/MW field gradient. We recently fabricated the ion trap chip integrated with a high-Q superconducting resonator, which can be applied to the ion trap experiment [7]. A microwave current is amplified by the high-Q superconducting resonator, and a power-efficient two-qubit gate will be achieved. We also discuss the other applications of the superconducting circuits to other isolated quantum systems. 
    
   Reference: 
   [1] S. B. Bravyi and A. Y. Kitaev, arXiv:9811052 (1998). 
   [2] Google Quantum AI, Nature 614, 676 (2023). 
   [3] V. V. Sivak, A. Eickbusch, B. Royer, S. Singh, I. Tsioutsios, S. Ganjam, A. Miano, B. L. Brock, A. Z. Ding, L. Frunzio, S. M. Girvin, R. J. Schoelkopf & M. H. Devoret, Nature 616, 50 (2023). 
   [4] A. G. Fowler, M. Mariantoni, J. M. Martinis, and A. N. Cleland, Phys. Rev. A 86, 032324 (2012) 
   [5] R. Sun, K. Makise, W. Qiu, H. Terai and Z. Wang, in IEEE Transactions on Applied Superconductivity, 25, 1 (2015). 
   [6] C. M. Löschnauer, J. Mosca Toba, A. C. Hughes, S. A. King, M. A. Weber, R. Srinivas, R. Matt, R. Nourshargh, D. T. C. Allcock, C. J. Ballance, C. Matthiesen, M. Malinowski, T. P. Harty, arXiv:2407.07694 (2024). 
   [7] Y. Tsuchimoto, I. Nakamura, S. Shirai and A. Noguchi, EPJ Quantum Technology 11, 56 (2024). 

1. Christian Haffner is a Principal Member of Technical Staff and the first one to receive IMEC’s tenure track. His tenure project investigates the fundamental limits of electro-optical devices for classical and quantum applications. In 2022, he received an ERC starting grant to support this research. In 2019, he joined the 5-year Branco-Weiss Fellowship program. He did his Postdoc research on nano-scale opto-mechanical switches at NIST, Gaithersburg and ETH, Zurich. He earned his Ph.D. degree from ETH Zurich in 2018, which was recognized with the ETH Medal and Hans-Eggenberger Prize. He received his B.Sc. and M.Sc. degree in electrical engineering from the Karlsruhe Institute of Technology (Germany)in 2012 and in 2013, respectively.
2. Atsushi Noguchi is Associate Professor at the University of Tokyo, and Team Leader of Riken Center for Quantum Computing. He received his Ph.D. for Ion Trap Quantum Technology from Osaka University in 2013. After a postdoctoral fellowship at Osaka University in 2014, he has working on hybrid quantum systems with superconducting circuits at RCAST, the University of Tokyo, since 2015. He has been an associate professor of the Department of Basic Science at the University of Tokyo since 2019. He is also a Fellow of InaRIS at Inamori Institute of Science from 2020, and a Team Leader at RIKEN Center for Quantum Computing from 2021.