Trapping Electrons in a Room-Temperature Microwave Paul Trap

Abstract

We demonstrate trapping of electrons in a millimeter-sized quadrupole Paul trap driven at 1.6 GHz in a room-temperature ultrahigh vacuum setup. Cold electrons are introduced into the trap by ionization of atomic calcium via Rydberg states and stay confined by microwave and static electric fields for several tens of milliseconds. A fraction of these electrons remain trapped longer and show no measurable loss for measurement times up to a second. Electronic excitation of the motion reveals secular frequencies that can be tuned over a range of several tens to hundreds of MHz. Operating a similar electron Paul trap in a cryogenic environment may provide a platform for all-electric quantum computing with trapped electron spin qubits.

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Plain Language Summary

An electron has only two quantum states, spin up and spin down, which makes it a natural candidate for a quantum bit. To enable control of its spin state, however, the electron needs to be kept in place. Electrons can be trapped by quantum dots, films of superfluid helium, or confined to the outer shell of atomic ions. But the addition of a confining structure adds extra degrees of freedom, complicating quantum control and often leading to decoherence. The ideal electron spin qubit would be isolated in vacuum, free from unnecessary interactions. Here, we introduce an experimental platform that allows for trapping individual electrons in vacuum.

We use a combination of rapidly oscillating and static electric fields to confine electrons inside an ultrahigh vacuum chamber at room temperature. The same technique is already used for trapped ion quantum computers, but electrons are much lighter than ions, so the trapping fields need to be at microwave frequencies instead of radio frequencies. Electrons are loaded into the trap by using two lasers to gently remove individual electrons from calcium atoms sent through the trapping region. When the ionization takes place inside the trapping region, we find that some electrons are confined for a few tens of milliseconds and then escape, while others remain trapped for probably many seconds.

Showing that it is possible to trap electrons in vacuum is the first step to using them as qubits. Building on the similarities with trapped ions, future work will be directed toward quantum control and readout of the electron spin states.