Applications of hybrid single-electron turnstiles: To current standards and beyond

Marco Marín Suárez

Research output: ThesisDoctoral ThesisCollection of Articles


Hybrid single-electron transistors formed of a normal-metal island and superconducting leads (SINIS) have been used for generating single-electron currents. These single-electron turnstiles (ST) are voltage biased while a periodical voltage modulation is applied to its gate electrode. Accuracy in current generation in this device is limited, however, investigation of the physics behind its operation has allowed applications beyond metrological purposes. For example, they serve as a probe of the concentration of superconducting excitations in its leads. In this thesis, these applications are used first by probing extraction of superconducting excitations generated in the leads of the device by its bare operation. These quasiparticles (QPs) are unpaired electrons in the superconducting condensate of Cooper-pairs. The extraction is done by voltage biased Josephson junctions which share one lead with the SINIS ST and have other with higher energy gap. A reduction of one order of magnitude in QP density is observed by using the deviation of the generated current as an accurate probe. Then, an extension of the SINIS ST applications is presented. By driving this device with a signal of frequency f, two QPs are created in the leads close to the energy gap Δ so that a power 2Δf is generated in total. This enables to envision the development of the SINIS ST into a standard for the unit of power. It is also shown that such power generation is possible even in the absence of net particle current at zero bias. Furthermore, an analysis about the ultimate possible accuracy of power generation in a simplified version of this device is presented in this thesis. It is seen that errors increase with increasing operation frequency, tunnel resistance, temperature and presence of sub-gap states. Additionally, it is shown that detection efficiency of QP energy can be >99% at typical cryogenic temperatures. Following this, it is shown that by injecting an extra modulation to the source electrode of the transistor, different driving trajectories can be drawn in its stability diagram. With this, a new driving method with twice the frequency applied to the drain-source bias compared to the one applied to the gate is proposed. By doing so, tunneling events occurring against the biased direction are suppressed. These tunneling events lower the current below the expected outcome. Accuracy of current generated by SINIS ST is increased by one order of magnitude using the new driving method. Furthermore, it is shown that a similar driving method can be used for generating single-electron currents at zero-average bias, which had not been investigated until now in SINIS STs.
Translated title of the contributionApplications of hybrid single-electron turnstiles: To current standards and beyond
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Pekola, Jukka, Supervising Professor
  • Peltonen, Joonas, Thesis Advisor
Print ISBNs978-952-64-1286-3
Electronic ISBNs978-952-64-1287-0
Publication statusPublished - 2023
MoE publication typeG5 Doctoral dissertation (article)


  • single-electron turnstile
  • quasiparticle extraction
  • frequency-to-power conversion
  • bias modulation


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