whereas a qubit can be in both states at the same time. In theory, this situation allows for a quantum calculation in which the operations are performed simultaneously for many possible computational pathways. In the case of a single qubit, this means zero and one, but as the number of qubits increases, the amount of possible numbers and
simultaneous calculations grows
exponentially. The quantum state of a qubit is very fragile and easily disturbed between and during the operations. The key to successful quantum calculation is being able to protect the qubit state from disturbances in the environment.
Entanglement According to quantum physics, two particles or objects can end up in a so-called entangled quantum state, where they share each others’ properties. The objects can in principle reside arbitrarily far away from each other. In particular, it appears that measuring one of them will instantaneously affect the other. One of the goals of Sillanpää is to observe entanglement between micromechanical resonators. “Although to some extent quantum entanglement has been proven, it has only ever been shown in small entities such as atoms and electrons,” he says. “What I would really like to do is to start trying to do this with things that are close to being visible with the naked eye. To even achieve this over
the distances of
around 1mm would be a tremendous achievement, but
this will not only take many years but also be highly challenging.”
Scanning electron micrograph showing the 5-microns-long and 4-microns- wide bridge-type mechanical resona- tor (dashed box) suspended on top of the qubit island. The state of the qubit is measured using a microwave cavity (blue).
Sillanpää is happy to admit that his
research is some way off of reaching practical applications. “This is really the epitome of basic research at the moment,” he says. “But the world is an interesting place and it is good to know the laws of physics and fundamental ways in which our universe works.” Although Sillanpää’s ERC project is basic
research aimed at understanding the laws of nature, there is a technological motivation in the distance: future quantum information processing. Micromechanical resonators can serve as an intermediator of quantum information from the quantum bits via optical fibers even to the other side of the Earth, which could form the basis of a quantum internet.
★
A superconducting quantum bit (spheres) can be made to interact with two different resonant cavities. A low frequency phonon cavity (vibrating string) can be used as a storage of quantum information from the qubit, whereas an electrical microwave resonator (represented by the mirrors) acts 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. Image by Juha Juvonen.
www.projectsmagazine.eu.com
AT A GLANCE Project Information
Project Title: CAVITYQPD: Cavity quantum phonon dynamics
Project Objective: The project involves experimental research in physics in order to test the theory of quantum mechanics at a scale close to everyday life. We will study vibrating micromechanical resonators and aim to investigate how the predictions of quantum physics can be tested in such systems.
Project Duration and Timing: 60 months, starting January 2015
Project Funding: ERC Consolidator Grant 2.0 Me
Project Partners: ERC Consolidator Grant 2.0 Me
MAIN CONTACT
Mika A. Sillanpää Prof. Mika A. Sillanpää got his PhD in 2005 in Helsinki University of Technology, Finland. He spent 2005-2007 as a postdoc in NIST, Colorado. Since 2010 he has worked as an independent PI at Aalto University, Finland. He has been awarded by two ERC grants: StG 2009, and CoG 2013.
Contact: Tel: +358 (0) 50 3447330 Email:
Mika.Sillanpaa@
aalto.fi Web:
http://physics.aalto.fi/
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