Investigating coherence of electrons on helium with cavity quantum electrodynamics

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Non-technical abstractElectrons have a unique interaction with liquid helium. Like mythological Narcissus, they are attracted to their own image, but they are prevented from entering the liquid. The competing forces, along with the quantum fluctuations cause the electrons to levitate several nanometers above the surface, where they form a pristine two-dimensional electron gas. The electrons are manipulated using electrodes underneath the surface to control their motion and eventually their spin. The electrons are promising candidates as qubits for quantum information processors and the research team is also investigating unique quantum many-body states they form known as Wigner molecules. Despite being one of the first discovered two-dimensional electron systems,there have been no detections or other studies of their spin properties. The team is using recently developed single electron motion and spin resonance techniques to perform these fundamental measurements. The project is developing a unique hybrid quantum system, in which electrons on helium interact with high finesse superconducting circuits, that can manipulate both single electrons and microwave photons.Technical DescriptionElectrons on helium present unique opportunities to study the dynamics individual electrons, their spins, and the excitations of superfluid thin films. This research will explore the extreme mobility and long coherence of this two-dimensional electron system using a novel cavity QED based architecture. This allows the project to leverage the past decade worth of advances in service of quantum information to study the fundamental excitations of this system. Similarly, electrons on helium themselves may have properties uniquely well-suited to quantum information and sensing applications. The motion of an electron on helium is very analogous to that of a superconducting qubit, so many of the same techniques can be used to interrogate them, which should allow coherent manipulation of their motion for the first time. This would be a unique type of cavity QED system that would allow one to gain insight into the properties and interactions of this unique two-dimensional electron system. The project is attempting to detect and achieve strong coupling to a single trapped electron. In addition, the team will build Wigner molecules by adding or removing individual electrons to a pool of helium. A single electron on helium will be trapped and coupled to the superconducting cavity. Calculations predict that this system will reach the strong coupling limit of cavity quantum electrodynamics (QED) where the electron can interact coherently with single photons. This is the first investigation of coherent properties of an isolated electron on helium. The spin properties of a single trapped electron are also being studied, and it appears possible that it too may reach the strong-coupling limit, where the spin-photon coupling exceeds the all relevant decoherence rates, and single photon storage and manipulation become possible. Measurements of the spin coherence times will reveal information about the magnetic environment as well as the electron-helium interactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.