Electron flying qubit as a new platform for quantum computation
Shintaro Takda
National Institute of Advanced Industrial Science and Technology (AIST), National Metrology Institute of
Japan (NMIJ), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan
Flying qubits implemented with optical photons are often used to exchange information within an engineered
quantum system, and they represent a vital part of the global roadmap towards secure data transmission. Due to
the weak interaction between bosons, two-qubit gates are challenging to implement with optical photons. We
propose an alternative approach for flying qubits with single electrons propagating ballistically in a semiconductor
quantum device [1-3]. This qubit architecture is defined in an electronic Mach-Zehnder interferometer (MZI),
where pseudo-spin states are defined by the presence or absence of an electron wave in one of the two paths of
the MZI [1]. Utilizing the Coulomb interaction which has no counterpart in photons, a two-qubit can also be
implemented [3]. Towards quantum information applications, it is desirable to operate the flying qubit with an
on-demand single-electron source. Among several single-electron sources [3], we study the one realized by
carrying an electron with a moving electric potential of surface acoustic waves (SAWs) [4] and also the one called
Leviton source realized by applying a Lorentzian voltage pulse on an Ohmic contact [5].
In this seminar, we first introduce our work associated with SAW. This includes the results of our recent work
on time-of-flight measurement of single flying electrons transferred by SAWs [6], single-electron transfer by a
compressed acoustic chirp pulse [7], and Coulomb mediated anti-bunching [8]. We also discuss our recent efforts
to realize a flying qubit with SAWs. Then we introduce our recent work associated with Leviton source. When
we excite an electron wave packet with a voltage pulse, the excited electron wave packet propagates along the
system as a plasmon, and its velocity is enhanced by interaction effect compared to non-interacting ballistic
electrons [9]. For the qubit control, the velocity is a key parameter, which depends on an eigenstate of the plasmon
and determines the spatial extension of an electron wave packet. We present the study of the plasmon velocity of
electron wave packets with several different spatial extensions in electron wave guides having several different
lengths. We find that the spatial extension of an electron wave packet plays an important role for the plasmon
velocity. The observation of quantum interference in a MZI operated with electron wave packets generated by
ultrashort voltage pulses, is also presented. We observe controlled quantum interference when injecting electron
wave packets into the MZI of a length of 14 μm. We observe a striking increase in the visibility of Aharonov-
Bohm oscillations when the temporal width of the wave packet is reduced. These results will pave the way for the
first demonstration of a flying electron qubit with ultrashort charge pulses at the single electron level.
1. M. Yamamoto, et al., Nature Nanotechnology, 7, 247–251 (2012).
2. C. Bäuerle, et al., Rep. Prog. Phys. 81 056503 (2018).
3. H. Edlbauer, et al., EPJ Quantum Technol. 9, 21 (2022).
4. S. Hermelin et al., Nature 477, 435, (2011).
5. J. Dubois, et al., Nature 502, 659-663 (2013).
6. H. Edlbauer et al., Applied Physics Letters 119, 114004 (2021).
7. J. Wang et al., Phys. Rev. X 12 031035 (2022).
8. J. Wang et al., Nature Nanotechnology 18, 721 (2023).
9. G. Roussely et al., Nature Communications 9, 2811 (2018).