2D Electrons on Liquid Helium under Irradiation
Electrons trapped on the surface of liquid helium present an extremely clean two-dimensional (2D) electron system. The quantized bound states of the electron orbtial motion perpendicular to the liquid surface (the Rydberg states) are formed due to interaction of an electron with its image charge in the liquid (see sketch on the right).
2D electrons on helium present a unique counterpart of two-dimensional electron gases (2DEGs) in semiconductors and have an unprecedently high mobility. Therefore, the transport propeties of this system, in particular under microwave irradiation, and comparison with those in semiconductors is of great interest.
Recently, it has been also realized that the orbital and spin states of electrons on helium is a promising potential resource for quantum information processing (QIP).
Microwave-Induced Quantum Transport
When 2D electrons are subject to a magnetic field applied perpendicular to the 2D plane, the energy of their lateral motion also becomes quantized into a set of equally-spaced Landau levels. Facinating transport phenomena occur when transtions beween different Landau levels are excited by externally applied microwave radiation. In particular, it leads to the Microwave-Induced Resistance Oscillations (MIRO) and Zero-Resistance States (ZRS), which were first observed in 2DEGs formed in GaAs/AlGaAs heterostructuers. Some outstanding open questions sill exist and prevent complete understanding of these phenomena in semiconductors, for example immunity of MIRO to the direction of circular polarization of radiation.
Since electrons on helium present an extremely clean counterpart of 2DEG in semiconductors, we study facinating phenomena of MIRO and ZRS in this system to resolve those open questions. In our experiments, we employ transport measurements using a capacitive-coupling technique, as well as microwave optical cavities to enhance effect of radiation.
R. Yamashiro, L. V. Abdurakhimov, A. O. Badrutdinov, Yu. P. Monarkha, and D. Konstantinov
A. A. Zadorozhko, Yu. P. Monarkha, and D. Konstantinov
Cavity QED with Electron Ensembles
Strong coupling regime of light-matter interaction bewteen quatum systems and photons in an optical cavity is a cornerstone of cavity Quantum Electrodynamics (cQED). Ability to coherently exchange excitations between two quantum fields has many appications in quatum technologies. Of particular recent interest is the interaction bewteen an ensemble of two-level atoms and a cavity mode, which shows enhancement in coupling stength compared to a single atom.
In our experiments, we realize the strong coupling between an ensemble of 2D electrons on helium and a single-mode Fabry-Perot cavity resonator working in a millimeter-wave frequency range. We are interested in the study of non-linearities in this coupled system and their potential use for creation of non-classical states of light and matter.
L. V. Abdurakhimov, R. Yamashiro, A. O. Badrutdinov, and D. Konstantinov
J. Chen, A. A. Zadorozhko, and D. Konstantinov
J. Chen, D. Konstantinov, and K. Molmer
Dressed Rydberg States in Quantizing Magnetic Fields
In magnetic fields applied perpendicular to the 2D plane, quantized lateral and transverse orbital motions of an electron are essentially uncoupled. However, coupling between them can be induced by an additional component of B-field applied parallel to the 2D plane. The Hamiltonian of coupled system is reminiscent of the famous Jaynes-Cummings model; in our case Rydberg states and Landau states of an electron play the roles of the two-level system and the photon field, respectively.
In our expeiriments, we create this situation by appling a B-field which is tilted with respect to the surface of liquid helium and perfoming the Stark spectroscopy of electron's energy levels. We find a variety of phenomena reminiscent of those studied in Atomic and Molecular Optics (AMO), such as sideband transitions, avoide crossings, Lamb shift, etc. We are interested in exploiting the non-linearity introduced by this coupling and performing cQED experiments with this system.
K. M. Yunusova, D. Konstantinov, H. Bouchiat, and A. D. Chepelianskii
Spin-Rydberg Intercation and Electron Spin Qubits
The interest in using quantum states of the electrons on liquid helium as quantum bits has been recently growing since the system is free of impurities and defects, which is an ideal platform with which to realize a quantum computer. In particular, spin states of the electrons on liquid helium are expected to have a longer coherence time than in any other materials.
We aim to experimentally demonstrate the indispensable functions of quantum computation such as read-out, control and initialization of the spin states of the electrons on helium using the interaction between the spin states and the Rydberg states.
Although the intrinsic spin-Rydberg interaction is vanishingly small, we could introduce an artificial one by a local magnetic field gradient which can be created by a current running through a superconducting wire in the vicinity of the trapped electrons or by a ferromagnet under an external magnetic field.
We are currently working on the read-out of the qubit states. Recently, we have proposed and experimentally demonstrated a new method to detect the transitions between different Rydberg states of the electrons, called image-charge detection. The image-charge detection can be readily extended to the detection of the transitions between Rydberg states of a single electron and can potentially be used to realize a nondestructive readout of the spin state of a single electron with the help of the spin-Rydberg interaction.
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