CORDIS

Realizing macroscopic quantum physics requires long mechanical coherence times and large masses in combination with well-controlled interactions between a macroscopic mechanical device and a quantum system. Current experiments lack at least one of these features. Our project follows the radically new approach to combine these requirements in a single integrated experimental platform: we will inductively couple superconducting mechanical oscillators, both levitated and suspended, to superconducting quantum circuits, thereby making use of the large magnetomechanical coupling and mechanical isolation that is achievable in such a configuration. In that way MaQSens will establish a new technological platform for quantum enabled mechanical devices with otherwise unachievable performance. Such superconducting magnetomechanical platforms will also exhibit exceptional sensitivity to accelerations and external forces, hence offering a new sensing technology of potential industrial relevance.
In the long term, our project paves the way for the next generation of macroscopic quantum experiments by establishing a game-changing technology. Our envisioned platform, quantum magnetomechanical devices with unprecedented coherence times and masses that are controlled via on-chip superconducting circuits, is unique and is believed to have properties thus far not anticipated in any other viable experimental architecture. This technology will allow addressing a plethora of fundamental questions in physics (examples include the intersection of gravity with quantum physics). At the same time, it will enable applications with unprecedented performance in the domain of sensing and information processing (examples include inertial, magnetic and force sensing, hybrid quantum information processing). MaQSens will establish European excellence as a kickstarter of this development.

Our ongoing work is being pursued along four main directions of research: (1) stable magnetic levitation of micrometer-sized superconducting objects, (2) quantum magnetomechanical coupling of mechanical motion to superconducting circuits, (3) quantum state control of mechanical motion by engineered magnetomechanical coupling, and (4) quantum magnetomechanics for fundamental tests and applications.
(1) stable magnetic levitation of micrometer-sized superconducting objects
Stable levitation of superconducting microparticles has been achieved both at 4 Kelvin and at milli-Kelvin temperatures. Different trapping architectures have been studied and levitation was successfully shown in a miniaturized 3-dimensional Anti-Helmholtz coil configuration. First levitation tests in a novel superconducting micro-chip geometry have also been performed. We have also developed methods to fabricate micron-sized superconducting particles of different shapes and have performed theoretical studies to investigate the influence of particle shape on the trapping characteristics. Measurements and optimization of both the mechanical dissipation and the seismic noise of the cryostat are currently underway.
(2) quantum magnetomechanical coupling of mechanical motion to superconducting circuits
In a first step, we have fabricated chip-based mechanical cantilevers that are compatible with coupling to superconducting circuits. We have also fabricated on-chip inductively coupled superconducting circuits (both qubits and cavities) that can couple to mechanical devices, and we have designed magnetic flux based detectors for mechanical readout. This effort recently culminated in the successful demonstration of magnetomechanical coupling to a superconducting waveguide. In ongoing work, we are striving to increase the magnetomechanical interaction to enter the regime of ultra-strong coupling.
(3) quantum state control of mechanical motion by engineered magnetomechanical coupling
Our consortium has developed theoretical toolboxes for engineering the levitation potential of superconducting micro-objects. Work is underway on designing quantum protocols that allow to observe mechanical quantum phenomena in the clearest and most efficient way. From the experimental side, the expected achievements from (1) and (2) will allow to demonstrate mechanical quantum state control. An initial step will be to demonstrate the quantum ground state of motion of the mechanical objects via magnetomechanical coupling.
(4) quantum magnetomechanics for fundamental tests and applications
We have developed first proposals on force sensing of ultra-small forces using magnetomechanical interactions. In a next step of this work, quantum-enabled protocols will be investigated.

The outstanding challenge that MaQSens is prepared to achieve is to implement quantum control in a regime of long coherence times, large masses and strong coupling. We go radically beyond the state-of-the-art by combining in a new way superconductors with quantum optomechanics. The superconducting mechanical object becomes an active and integral element in the superconducting quantum circuit, for which exceptional
quantum control has already been achieved. This has two dramatic consequences:
(i) By inductively coupling a superconducting cantilever to a superconducting qubit we expect to reach the single- (microwave) photon strong coupling regime.
(ii) By combining magnetic levitation with magnetic coupling to superconducting circuits we will profit from extremely long coherence times (we target trap frequencies in the 1,000-10,000 Hz range with Q factors > 1e10 using type I superconductors) and large masses (>1e13 a.m.u.). Both scenarios will result in exceptional controllability of the combined quantum system.

If successful, MaQSens will open up a completely new parameter regime for macroscopic quantum physics experiments, covering unprecedented large masses (>1013 a.m.u.) and long coherence times (> 1ms) in an architecture that offers full quantum control. This opens up a completely new generation of fundamental physics studies of macroscopic quantum phenomena. Other areas of relevance include the scientific foundation of magnetic levitation of micron-scale superconductors as well as high-precision tests of fundamental forces such as gravity or Casimir forces. Finally, the most fascinating avenue with the highest potential impact is certainly the investigation of quantum effects under the influence of gravity. The expected sensitivity to external forces of our superconducting magnetomechanical platform also opens a plethora of possible quantum-based sensing applications. Concerning impact on society, a success of MaQSens will generate an important contribution to the understanding of fundamental physics laws, an impact that would benefit all society. The consortium, comprising partners from both academia and industry, also contributes directly to the still uncommon dialogue between the fundamental sciences and industry. Finally, by operating at the forefront of modern quantum science and technology and by keeping close to industrial applications, MaQSens will empower new and high-potential actors for their future roles as technological leaders in academia and industry.