The NEMS group is officially affiliated by the Department of Applied Physics, under the name Quantum Nanomechanics. Our laboratory is situated in the O.V. Lounasmaa Laboratory/Low Temperature Laboratory.
We focus on studies of micromechanical and nanomechanical resonators near the quantum ground state of moving objects. We aim on observing quantum superposition states of motion by coupling vibrating beams to quantum electrical circuits built upon superconducting junctions or resonators. We also investigate quantum phenomena in such superconducting junction qubits.
- Mika Sillanpää, Ph.D., Associate Professor
- Matthias Brandt, Ph.D.
- Jian Li, Ph.D.
- Juha-Matti Pirkkalainen, M.Sc., Ph.D. student
- Jaakko Sulkko, Mr., M.Sc. student
- Erno Damskägg, Mr., M.Sc. student
- Mikael Kervinen, Mr., M.Sc. student
The NEMS group is constantly seeking motivated and capable students to join the team. We are looking for summer students, Master's students, as well as Ph.D. students.
Nature paper published 14.2.2013: "Hybrid circuit cavity quantum electrodynamics with a micromechanical resonator", Nature 494, 211–215 (2013) .
by J.-M. Pirkkalainen, S. U. Cho, Jian Li, G. S. Paraoanu, P. J. Hakonen, and M. A. Sillanpää
A superconducting quantum bit, or, qubit (green) is coupled to a micromechanical oscillator (spring). The state of the qubit is measured using a microwave cavity (blue). On the right, the state of the qubit is transferred to mechanical motion such that the oscillator is in two places simultaneously.
15th Dec 2011
(image Juha Juvonen)
A possibility was demonstrated to detect and amplify microwaves near the Heisenberg uncertainty principle limit with a micromechanical device.
Our work 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.
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 have recently achieved 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. We obtained a low number of about twenty thermal phonon occupation at the equilibrium bath temperature at 25 mK. The mechanical properties of Aluminum were excellent after FIB cutting and we recorded a quality factor of Q ~ 300 000 for a 67 MHz resonator at a temperature of 25 mK.
Nanomechanics coupled to superconducting qubits
Quantum systems with different degrees of freedom can be integrated to produce different properties. We have made a system that combines a quantum memory element, which has long-lived quantum states, with a quantum interface that offers easy read-out. This is achieved by coupling an artificial atom, known as a superconducting transmon qubit, into a microwave resonator and a nanomechanical resonator.
We that this system represents a prototype of a quantum interface. The microwave resonator allows access to the qubits, whereas the nanomechanical resonator could enable the conversion of quantum information between microwave radiation and mechanical motion. The nanomechanical resonator can be used to store quantum information in long-lived states.
Graphene mechanical resonators
Our theory proposal for Macroscopic Quantum Tunneling (MQT) in graphene Phys. Rev. B 84, 195433 (2011) covered in Science.
We suggest that quantum tunneling can take place in a basic phenomenon known from micro- or nano electromechanical devices, namely, in the collapse of a suspended membrane due to applied voltage.
The collapse occurs when the voltage exceeds a certain critical value. Just before this pull-in takes place, the potential energy of the membrane has two (meta)stable minima, corresponding to two different positions - uncollapsed and collapsed. At low enough temperatures, the macroscopic displacement consisting of millions of atoms forming the membrane may tunnel through the potential barrier.
Superconducting phase qubits and transmon qubits
Together with National Institute of Standards and Technology (Boulder, Colorado) and VTT, we investigate single and cavity-coupled phase qubits.
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- Maria Berdova, M.Sc.
- Meri Helle, Dr.Tech.
- Sung Un Cho, Ph.D.
Our research is supported by the European Research Council, and by the Academy of Finland.