Department of Applied Physics

Quantum Nanomechanics

The Quantum Nanomechanics group focuses on the quantum-mechanical behavior of macroscopic moving objects, using micro- and nanomechanical resonators at the ground state of motion. In our unique efforts, we seek to experimentally address the elusive interface between quantum mechanics and gravity. We also use superconducting qubits with micro acoustics for quantum technology, and explore the coupling of spin waves to acoustics.
The group is part of the national Centre of Excellence – Quantum Technology Finland (QTF).
An illustration of the 15-micrometre-wide drumheads prepared on silicon chips used in the experiment. The drumheads vibrate at a high ultrasound frequency, and the peculiar quantum state predicted by Einstein was created from the vibrations. Image: Aalto University / Petja Hyttinen & Olli Hanhirova, ARKH Architects.


Hands touching an art piece on the quantum exhibition.
Studies Published:

InstituteQ launches new doctoral school in quantum technology

The Doctoral School in Quantum Technology and the industrial doctorates are now in operation
The InstituteQ logo on black background
Cooperation, Press releases, Research & Art Published:

Finnish Quantum Agenda details road ahead and stresses need for national quantum strategy

What are Finland’s strengths in quantum technology? How can Finland ensure it stays on top of the groundbreaking changes quantum technology will cause in the coming years and decades? These are the questions the Finnish Quantum Agenda answers.
Vivian Phan leaning on a grey wall
Studies Published:

“Have the tenacity and believe in your progress" – Studying quantum, the field of the future, now

Vivian Phan is a BSc graduate of Aalto University’s Quantum Technology studies and worked as part of the Micro and Quantum Systems research group. She shares what it’s like to build a career in a field that’s new and will most likely have its biggest impact years or decades from now.
The drumheads exhibit a collective quantum motion. Picture: Juha Juvonen.
Press releases Published:

Aalto researchers awarded Physics World Breakthrough of the Year for macroscopic quantum entanglement

Aalto University Professor Mika A. Sillanpää, his team and collaborators at the University of New South Wales in Canberra, Australia, have won the Physics World 2021 Breakthrough of the Year. The prize was awarded for establishing quantum entanglement between a pair of macroscopic drumheads – two mechanical resonators that were tiny but still much larger than the subatomic particles that are usually entangled. The award has previously been given for the first direct observation of a black hole and for the detection of gravitational waves, which also received a Nobel Prize.
Professor Mika Sillanpää

Group leader

Prof. Mika Sillanpää

Entangled mechanical oscillators

Entanglement is perhaps the most intriguing feature of quantum mechanics. It allows objects to affect each other across arbitrary distances without any direct interaction, defying both classical physics and our common-sense understanding of reality. Entanglement is now commonly observed in experiments with microscopic systems such as light or atoms, and is also the key resource for quantum technologies such as quantum computation, cryptography and measurement.

Quantum entanglement is, however, extremely fragile, and it will disappear if the entangled particles interact with their surroundings, through thermal disturbances, for example. For this reason, entanglement between the motion of macroscopic objects has long been an elusive goal.

In recent works we created and stabilised entanglement between the center-of-mass motion of two drumhead resonators. The drumheads, 15 micrometer in diameter, are capacitively coupled to a single microwave "cavity" formed by a superconducting circuit. By driving the system with suitable microwave fields, we cool the thermal disturbances and bring the drumheads to a steady state where they are entangled indefinitely. Our work qualitatively extends the range of entangled physical systems and has implications for quantum information processing, precision measurements and tests of the limits of quantum mechanics.

Artist's impression of entangled drums.

Artist's impression of entangled vibrating drums. Image credit: Juha Juvonen.

Gravitational coupling within a quantum system

In this project, the goal is to touch a hundred-year-old mystery of physics: Despite its success at describing phenomena in the low-energy limit, quantum mechanics is incompatible with general relativity that describes gravity and huge energies. The interface between these two has remained experimentally elusive, because only the most violent events in the universe have been considered to produce measurable effects due to the plausible quantum behavior of gravity. We aim at detecting gravitational forces for the first time within a quantum system. We use thin membrane oscillators loaded by milligram masses and bring two such gravitationally interacting oscillators into nonclassical motional states. Initially, we will measure the gravitational force between gold particles weighing a milligram, representing a new mass scale showing gravitational forces within a system. This work is part of the ERC Advanced Grant project “GUANTUM: Probing the limits of quantum mechanics and gravity with micromechanical oscillators”.

    Gravitational coupling between nonclassical masses

    In the experiment, gold spheres of 1 milligram mass rest on a very thin membrane so that the spheres are close to each other but free to vibrate, and the same time, interact through gravity.

    vibrating gold sphere

    Mode profile of the fundamental drum mode of around 2 kHz frequency. The 1 mg gold sphere vibrates up and down.

    little gold spheres

    Gold spheres of 0.5 mm diameter have appreciable gravitational interaction at center-of-mass distances in mm range.

    Microwave optomechanics

    Quantum Backaction Evading Measurements

    The standard quantum limit constrains the precision of an oscillator position measurement. It arises from a balance between the imprecision and the quantum backaction of the measurement. Some measurement techniques, however, rely on coupling a probe to the system in such a way that the measured observable is an invariant of the Hamiltonian evolution, which allows to preserve the state of at least this observable. These are often called quantum nondemolition measurements, or quantum backaction evading (BAE) measurements. An example is the measurement of only a single quadrature of the oscillator, which can evade the backaction and thus can be carried out with arbitrary precision.

    We have extended the scope of BAE measurements to a new class of systems with a high degree of coherence and therefore immediately adapted to force or metric sensing. As the mechanical oscillator, we use a large 0.5 mm diameter silicon nitride (SiN) membrane oscillator with 707 kHz frequency, embedded in a microwave cavity. High-stress SiN has emerged as the material to realize the highest mechanical quality factors for usage in quantum optomechanics. The measurement shows that quantum backaction noise can be evaded in the quadrature measurement of the motion of a large object.

    We have demonstrated quantum backaction evading measurements of a collective quadrature of two mechanical oscillators, both coupled to a common microwave cavity. The work allows for quantum state tomography of two mechanical oscillators, and provides a foundation for macroscopic mechanical entanglement and force sensing beyond conventional quantum limits.

    Microwave signal processing

    Besides studying fundamental quantum concepts such as entanglement and backaction evasion, microwave optomechanics can be utilized for signal processing.

    We have demonstrated that microwave optomechanical systems can be used as ultra-low-noise microwave amplifiers. In a phase-preserving mode the incoming microwave signal can be amplified while adding only half a quantum of noise, the minimum amount required by Heisenberg's uncertainty principle. When configured as a phase-senstive amplifier, the device amplifies a single quadrature of the incoming signal while adding almost no noise at all. The novel type of amplifiers may offer improved performance for information processing in certain applications.

    Additionally, we have investigated nonreciprocal (i.e., directional) transport and amplification of electromagnetic or mechanical signals.

      Examle of a drumhead resonator

      Example of a drumhead resonator, imaged with a scanning electron microscope 

      Two microwave LC cavities coupled to a single mechanical drumhead resonator.

      Schematic of a sample with two microwave LC cavities coupled to a single mechanical drumhead resonator.

      Two drum oscillators and two cavities

      A device patterned lithographically on a quartz chip. The structure, made of thin film of superconducting aluminum, supports two microwave resonance modes, and includes two drum oscillators marked with the dashed line.

      Membrane resonator in a 3D cavity

      Silicon nitride drum resonators with quality factors up to 108 can be operated by embedding in 3-dimensional microwave cavity resonator, which allows for accessing and manipulating the motion of the membrane down to the quantum level.

      Micro acoustics coupled to superconducting qubits

      Quantum systems with different types of degrees of freedom can intertwine, forming hybrid states with intriguing properties. We have explored setups for coupling transmon qubits to either low-frequency flexural resonators, or GHz-regime micro acoustic overtone (HBAR) resonances.

      In a HBAR system, the modes mostly reside in the substrate chip and hence feature diluted strain and low acoustic losses. The system exhibits a dense spectrum of acoustic modes that interact near resonance with the qubit, suggesting a possibility to manipulate the many-mode system through the qubit. We have shown a qubit-HBAR system by controlling the qubit with longitudinal fields, allowing individually access a large number of acoustic modes.

        HBAR qubit.

        Assembly of a high-overtone bulk acoustic wave resonator (blue) on top of the Xmon qubit. The acoustic medium is a sapphire crystal that is first covered by a thin layer of molybdenum (60 nm), on top of which there is an approximately 1-micron-thick layer of polycrystalline aluminum nitride. The piezoelectric AlN layer acts as a transducer between the electric field of the qubit and the acoustic modes.

        transmon qubit and bridge resonator.

        Right: Scanning electron micrograph showing a 5-micron-long and 4-micron-wide bridge-type mechanical resonator (dashed box).

        Magneto acoustics

        We integrate magnetic materials with nano- and micromechanical devices to advance fundamental science and to obtain new functionalities that can lead to disruptive technologies. We study strain-mediated interactions between magnons and phonons in magnetic mechanical oscillators. The hybrid potential is provided by magnetostriction, which couples mechanical strain to magnetization. This activity can be regarded as an analog to cavity optomechanics, with magnons replacing the electromagnetic cavity.

        Latest publications

        Progress Toward Detection of Individual TLS in Nanomechanical Resonators

        Richard Pedurand, Ilya Golokolenov, Mika Sillanpää, Laure Mercier de Lépinay, Eddy Collin, Andrew Fefferman 2024 Journal of Low Temperature Physics

        Mechanical Resonators at Low Temperatures

        Eddy Collin, Mika A. Sillanpää 2023 Journal of Low Temperature Physics

        Special Issue on Mechanical Resonators at Low Temperatures

        Eddy Collin, Mika Sillanpää 2023 Journal of Low Temperature Physics

        Coupling high-overtone bulk acoustic wave resonators via superconducting qubits

        Wayne Crump, Alpo Välimaa, Mika A. Sillanpää 2023 Applied Physics Letters

        Fast Feedback Control of Mechanical Motion Using Circuit Optomechanics

        Cheng Wang, Louise Banniard, Laure Mercier De Lépinay, Mika A. Sillanpää 2023 Physical Review Applied

        Quantum backaction evading measurements of a silicon nitride membrane resonator

        Yulong Liu, Jingwei Zhou, Laure Mercier De Lépinay, Mika A. Sillanpää 2022 New Journal of Physics

        Multiphonon Transitions in a Quantum Electromechanical System

        Alpo Välimaa, Wayne Crump, Mikael Kervinen, Mika A. Sillanpää 2022 Physical Review Applied

        A macroscopic object passively cooled into its quantum ground state of motion beyond single-mode cooling

        D. Cattiaux, I. Golokolenov, S. Kumar, M. Sillanpää, L. Mercier de Lépinay, R. R. Gazizulin, X. Zhou, A. D. Armour, O. Bourgeois, A. Fefferman, E. Collin 2021 Nature Communications

        Microwave single-Tone optomechanics in the classical regime

        Ilya Golokolenov, Dylan Cattiaux, Sumit Kumar, Mika Sillanpää, Laure Mercier De Lépinay, Andrew Fefferman, Eddy Collin 2021 New Journal of Physics

        Energy-level attraction and heating-resistant cooling of mechanical resonators with exceptional points

        Cheng Jiang, Yu Long Liu, Mika A. Sillanpää 2021 Physical Review A
        More information on our research in the Aalto research portal.
        Research portal
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