An on-chip microwave resonator can be capacitively coupled to a nanomechanical resonator, similarly as in an optical cavity with a movable end mirror. In the dispersive limit where the LC (“cavity”) frequency is much higher than the mechanical frequency which usually is in the radio-frequency regime, the mechanical motion couples to the electrical frequency.
We achieve a large cavity coupling energy of up to (2 pi) 2 MHz/nm for metallic beam resonators at tens of MHz. We used focused ion beam (FIB) cutting to produce uniform slits down to 10 nm, separating patterned resonators from their gate electrodes, in suspended aluminum films.
Our recent work, done at the OVLL/Low Temperature Laboratory, indicates that it is possible to make a nearly noiseless amplifier based on a moving part measuring less than a tenth of the diameter of a hair. This kind of device is known as a nanomechanical resonator, resembling a miniaturized guitar string. The vibrations get amplified in an accompanying cavity, as in guitar’s resonant chamber in the picture, thus launching a stronger tone that comes in. The novel type of amplifiers may offer improved performance for information processing in certain applications.
Micromechanical resonators coupled to superconducting qubits
Quantum systems with different types of degrees of freedom can intertwine, forming hybrid entangled quantum states with intriguing properties. We have merged three quantum systems: a superconducting qubit (spheres) interacting with two different resonant cavities. A low frequency phonon cavity (vibrating string) was used as a storage of quantum information from the qubit, whereas an electrical microwave resonator (represented by the mirrors) acted as a means of communicating to the outside world. The idea could be used as a building block in the emerging field of quantum information and communication, as well as to enable creation of Schrödinger cat-like non-classical displacement states.
Scanning electron micrograph showing the 5-mm-long and 4-mm-wide bridge-type mechanical resonator (dashed box) suspended above the qubit island.
Superconducting phase qubits and transmon qubits
Together with the Low Temperature Laboratory, the National Institute of Standards and Technology (Boulder, Colorado) and VTT, we investigate single and cavity-coupled phase qubits.