{"id":2822,"date":"2026-07-02T01:37:27","date_gmt":"2026-07-01T16:37:27","guid":{"rendered":"http:\/\/www.quantum.ee.e.titech.ac.jp\/index.php\/en\/research\/"},"modified":"2026-10-06T18:54:15","modified_gmt":"2026-10-06T09:54:15","slug":"research","status":"publish","type":"page","link":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/en\/research\/","title":{"rendered":"Research"},"content":{"rendered":"\n<div class=\"kl-page\" lang=\"en\"><div class=\"kl-intro\"><p class=\"kl-eyebrow\">Kodera Laboratory<\/p><h1>Research<\/h1><p class=\"kl-lead\">We develop semiconductor quantum devices and the technologies needed to fabricate, control, read out and integrate them.<\/p><\/div><nav class=\"kl-topic-nav\" aria-label=\"Research topics\"><a href=\"#readout\">Scalable spin-qubit readout<\/a><a href=\"#autotuning\">Automated tuning with machine learning<\/a><a href=\"#rf\">Radio-frequency reflectometry<\/a><a href=\"#silicon-holes\">Hole-spin control in silicon<\/a><a href=\"#triangular-dots\">Triangular triple quantum dots<\/a><a href=\"#long-range\">Long-range interactions<\/a><a href=\"#device-design\">Device structures for integration<\/a><a href=\"#architectures\">Two-dimensional qubit architectures<\/a><a href=\"#cryo-cmos\">Cryogenic CMOS and quantum-device integration<\/a><a href=\"#germanium\">Germanium quantum dots<\/a><a href=\"#transport\">Single-electron transport with acoustic waves<\/a><a href=\"#noise\">Noise spectroscopy and correlations<\/a><a href=\"#hot-qubits\">Silicon qubits at elevated temperatures<\/a><\/nav><section class=\"kl-section\" id=\"readout\"><h2>Scalable spin-qubit readout<\/h2><p>Spin-to-charge conversion makes a spin state accessible to electrical measurement. We study low-noise cryogenic amplification and charge sensing, with attention to bandwidth, power dissipation, wiring and the space available inside a refrigerator. Our aim is to develop readout systems that can be extended to larger numbers of qubits.<\/p><\/section><section class=\"kl-section\" id=\"autotuning\"><h2>Automated tuning with machine learning<\/h2><p>Each quantum-dot device requires careful adjustment of gate voltages. We investigate machine-learning methods, including model-based reinforcement learning, to automate this process. Our work includes constructing environment models from silicon quantum-dot measurement data and developing methods that can be extended to more complex devices.<\/p><\/section><figure class=\"kl-figure\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/www.quantum.ee.eng.isct.ac.jp\/wp-content\/uploads\/C_KondoAI_Fig1.jpeg\" alt=\"Model-based reinforcement learning for automated quantum-dot tuning\"><figcaption>Automated tuning with model-based reinforcement learning. See Kondo et al., APL Machine Learning 3, 016114 (2025).<\/figcaption><\/figure><section class=\"kl-section\" id=\"rf\"><h2>Radio-frequency reflectometry<\/h2><p>RF reflectometry measures changes in a device\u2019s electrical response through a matching circuit. We study tunable impedance matching at cryogenic temperatures, mixed-mode transmission to reduce crosstalk, and matching circuits for frequency multiplexing. Current work also covers IQ-encoded readout, parametric amplification and cryogenic oscillators.<\/p><\/section><figure class=\"kl-figure\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/www.quantum.ee.eng.isct.ac.jp\/wp-content\/uploads\/rf.png\" alt=\"RF reflectometry measurement setup\"><figcaption>An RF reflectometry measurement setup used to detect changes in a quantum-dot device.<\/figcaption><\/figure><section class=\"kl-section\" id=\"silicon-holes\"><h2>Hole-spin control in silicon<\/h2><p>We investigate hole spins in physically defined p-type silicon quantum dots fabricated by etching silicon-on-insulator substrates. Spin\u2013orbit coupling offers a route to electrical spin control without additional magnetic structures. We study device designs and operating conditions that support integration and operation at higher temperatures.<\/p><\/section><section class=\"kl-section\" id=\"triangular-dots\"><h2>Triangular triple quantum dots<\/h2><p>Three quantum dots arranged in a triangle provide a small building block for two-dimensional integration. We fabricate silicon devices and develop charge sensing, pulsed measurements and RF single-electron-transistor techniques toward fast spin readout. These measurements give access to individual tunnelling events and the dynamics of confined carriers.<\/p><\/section><section class=\"kl-section\" id=\"long-range\"><h2>Long-range interactions<\/h2><p>Coupling distant qubits is a challenge as quantum processors grow. We investigate interactions between the outer dots of serial triple quantum-dot devices in silicon, exploring routes beyond interactions between nearest neighbours.<\/p><\/section><section class=\"kl-section\" id=\"device-design\"><h2>Device structures for integration<\/h2><p>Physically defined silicon quantum dots can reduce the number of gates needed to form a device. We model electrostatic potentials and carrier distributions in silicon-on-insulator structures to guide device geometry, fabrication and measurement.<\/p><\/section><section class=\"kl-section\" id=\"architectures\"><h2>Two-dimensional qubit architectures<\/h2><p>We study arrangements of Si\/SiGe quantum dots for larger quantum processors, including architectures for noisy intermediate-scale quantum systems. This work is carried out with collaborators at RIKEN and considers how the small footprint of semiconductor spin qubits can support two-dimensional integration.<\/p><\/section><section class=\"kl-section\" id=\"cryo-cmos\"><h2>Cryogenic CMOS and quantum-device integration<\/h2><p>Room-temperature control electronics and their wiring place thermal and spatial demands on cryogenic systems. In collaboration with the Nagata\u2013Miki laboratory at Kobe University, we study the integration of silicon quantum-dot devices with cryogenic CMOS circuits. Our work includes flip-chip connections to active interposers with electrostatic-discharge protection and selector circuits.<\/p><\/section><figure class=\"kl-figure\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/www.quantum.ee.eng.isct.ac.jp\/wp-content\/uploads\/Interposer-scaled.jpg\" alt=\"Conventional wiring and flip-chip mounting on an active silicon interposer\"><figcaption>Device integration using an active silicon interposer. See Higashimomo et al., Jpn. J. Appl. Phys. 65, 03SP19 (2026).<\/figcaption><\/figure><section class=\"kl-section\" id=\"germanium\"><h2>Germanium quantum dots<\/h2><p>Germanium hole systems combine a small effective mass with strong spin\u2013orbit coupling. We fabricate and characterize germanium quantum dots, aiming to improve device performance and develop structures suitable for integrating hole-spin qubits.<\/p><\/section><section class=\"kl-section\" id=\"transport\"><h2>Single-electron transport with acoustic waves<\/h2><p>Surface acoustic waves can provide a way to move individual electrons between separated quantum dots. We aim to develop this approach in silicon, exploring a potential connection between local quantum devices and more distributed quantum-information architectures.<\/p><\/section><section class=\"kl-section\" id=\"noise\"><h2>Noise spectroscopy and correlations<\/h2><p>Understanding noise is essential for improving qubit control and device design. We analyze noise spectra in individual silicon quantum dots, correlations between dots, and fluctuations associated with interdot tunnelling. These measurements help distinguish sources of noise and guide the design of integrated devices.<\/p><\/section><section class=\"kl-section\" id=\"hot-qubits\"><h2>Silicon qubits at elevated temperatures<\/h2><p>We aim to operate silicon spin qubits at approximately 1\u20132 K, above the temperatures commonly used in spin-qubit experiments. Higher operating temperatures could allow more cooling power for nearby electronics. We investigate spin dynamics, operating points that preserve quantum information, and the relative advantages of electron and hole systems.<\/p><\/section><section class=\"kl-section\" id=\"papers\"><h2>Related publications<\/h2><p>Find the original papers, authors and publication details in our <a href=\"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/en\/publications\/\">publication list<\/a>. The <a href=\"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/study\/theme-2\/\">Japanese research page<\/a> includes additional experimental figures and references.<\/p><\/section><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Kodera Laboratory Research We develop semiconductor quantum devices and the technologies needed to fabricate,  [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":2821,"menu_order":21,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2822","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/pages\/2822","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/comments?post=2822"}],"version-history":[{"count":2,"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/pages\/2822\/revisions"}],"predecessor-version":[{"id":3096,"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/pages\/2822\/revisions\/3096"}],"up":[{"embeddable":true,"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/pages\/2821"}],"wp:attachment":[{"href":"https:\/\/www.quantum.ee.eng.isct.ac.jp\/index.php\/wp-json\/wp\/v2\/media?parent=2822"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}