Trapped Electrons as Charge Qubits

by Dr Markus Fleck (RIKEN)

Friday 25 Jul 2025, 15:00 → 16:00 Europe/Vienna

Besprechungsraum 1 (PSK)

There have been many different ideas for implementing quantum computing over time, some approaches even see somewhat wide-spread commercial usage today, such as Paul-trap-based ion qubits or quantum circuit dynamics-based superconducting qubits. But both approaches have their individual shortcomings, ion-based qubits tend to be slow and need sophisticated laser systems as well as fast particle shuttling techniques, while superconducting qubits are very sensitive to outside influences, and their quantum states are fragile, limiting their coherence times.

Our target is a synthesis of both approaches that addresses some of those issues. In circuit-based quantum computing, the basic building block is the charge qubit, a qubit based on charge states in a circuit that shows quantum effects, such as a Josephson Junction. The earliest approach for this is the Cooper-Pair box, nowadays the object if interest is the transmon. The transmon and associated circuits are rather successful for quantum computers with some 100s of qubits, since they can be easily replicated. They also allow for the usage of efficient logical qubit encodings, further  improving error resilience.

However, the transmon is approaching its limit on the coherence time, the time the quantum information in the qubit is preserved. So where to go from here? This is where trapped charged particles come in. A singly-charged particle confined in a Penning trap can be rather accurately described as a resonant circuit, with the inductance and capacitance depending only on the parameters of the trap and the used particle. Besides the usual imperfections, this system behaves very much like a quantum harmonic oscillator.

In precision measurements, we strive towards better and better harmonicity, but what happens if we intentionally make the trapping field anharmonic? In this case, the single particle quantum harmonic oscillator becomes a non-linear oscillator with properties remarkably similar to that of circuit-based charge qubit. So if we confine an electron in such a potential, the result would be a near-perfect charge qubit that's fairly decoupled from the noise sources that plague superconducting qubits. In this talk I'll introduce our work towards the floating charge qubit, the current state and future perspectives.

Zoom Details : 

https://cern.zoom.us/j/68123150949?pwd=UHsy8vZUJxz3bXgpmajR8tbnekRdEa.1

Meeting ID: 681 2315 0949
Passcode: 790651