Research areas

We work on a variety of topics in theoretical and mathematical physics. Some of the areas we focus on are:

• Mechanical systems in the quantum regime
  Our research involves theoretical studies of optomechanical or electromechanical setups with a focus on controlling micromechanical oscillators in the quantum regime, motivated in part by applications such as accurate sensing or quantum signal processing. We are also interested in the interplay of mechanical and transport properties in low-dimensional materials, e.g., graphene or topological materials.

• Macroscopic nonclassicality
  We are interested in nonclassicality witnesses, in particular for revealing quantum behaviour of systems excited to large numbers of quanta, i.e., high-intensity electromagnetic fields, or of mechanical degrees of freedom at the mesoscopic or macroscopic mass scale. This is motivated both by realization of robust quantum applications as well as fundamental issues, such as alternative theories of decoherence or the relation between quantum mechanics and gravity.
• Foundations of quantum mechanics
  Much of our research in this area is centred around quantum measurements: weak measurements, sequential measurements, symmetry-constraints, incompatibility. Other interests include the quantum-classical transition, quantum reference frames, contextuality, and general probabilistic theories.

Positions

Please feel free to contact us if you are interested in our research.

We may be able to welcome exchange students who wish to write their Master thesis with us. Please get in touch if this is of interest to you.

External funding

Our group has received funding through QuantERA - a European Research Area Network (ERA-NET) Cofund Programme in the field of Quantum Technologies. USN participates in two QuantERA projects: QuaSeRT (Optomechanical quantum sensors at room temperature, 2018-2021) and MQSens (Quantum sensing with nonclassical mechanical oscillators, 2022-2025).

Recent publications

• Quantum limits on squeezing
  X. Zhou, F. Massel
  arXiv:2604.22500

• Witnesses of genuine multipartite entanglement and nonlocal measurement back-action for Raman-scattering quantum systems
  K. R. Bush, K. Børkje
  Physical Review A 113, 032436 (2026), arXiv:2511.17211

• Interpreting quantum reference frame transformations through a simple example
  E. Castro-Ruiz,  T. D. Galley, L. Loveridge
  arXiv:2508.09540

• Gravity-mediated entanglement via infinite-dimensional systems
  S. L. Ludescher, L. Loveridge, T. D. Galley, M. P. Müller
  J. Phys. A: Math. Theor. 59 215302 (2026), arXiv:2507.13201

• Preparation of conditionally-squeezed states in qubit-oscillator systems
  M. K. Hope, J. Lidal, F. Massel
  arXiv:2504.01664

• Uncertainty relations relative to phase-space quantum reference frames
  M. J. Riera, L. Loveridge
  Physical Review A 111, L060201 (2025), arXiv:2411.08589

• Operational quantum reference frame transformations
  T. Carette, J. Glowacki, L. Loveridge
  Quantum 9, 1680 (2025), arXiv:2303.14002

• Skew Hecke algebras
  J. Waldron, L. Loveridge
  Communications in Algebra 53, 4624 (2025), arXiv:2311.09038

• Non-Hermitian topology and entanglement in an optomechanical superlattice
  W. Brzezicki, T. Hyart, F. Massel
  Physical Review Research 7, 013089 (2025), arXiv:2406.00137

• Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory
  C. J. Fewster, D. W. Janssen, L. Loveridge, K. Rejzner, J. Waldron
  Communications in Mathematical Physics 406, 19 (2025), arXiv:2403.11973

• Optomechanics Driven by Noisy and Narrowband Fields
  L. Banniard, C. Wang, D. Stirpe, K. Børkje, F. Massel, L. de Lepinay, M. Sillanpää
  Journal of Low Temperature Physics 217, 720 (2024), arXiv:2406.00546

• Ground-state cooling of a mechanical oscillator by a noisy environment
  C. Wang, L. Banniard, K. Børkje, F. Massel, L. de Lepinay, M. Sillanpää
  Nature Communications 15, 7395 (2024), arXiv:2306.15746

• Quantum Reference Frames on Finite Homogeneous Spaces
  J. Glowacki, L. Loveridge, J. Waldron
  Int. J. Theor. Phys. 63, 137 (2024)

• Hybrid optomechanical superconducting qubit system
  J. Manninen, R. H. Blick, F. Massel
  Phys. Rev. Res. 6, 023029 (2024)

• Semiclassical dynamics of a superconducting circuit: chaotic dynamics and fractal attractors
  D. Stirpe, J. Manninen, F. Massel
  Physica Scripta 99, 075979 (2024)

• Proposal for observing nonclassicality in highly excited mechanical oscillators by single photon detection
  K. R. Bush, K. Børkje
  Phys. Rev. A 109, 043505 (2024)

• Measurement disturbance and conservation laws in quantum mechanics
  M. H. Mohammady, T. Miyadera, and L. Loveridge
  Quantum 7, 1033 (2023)

• Non-Hermitian topological quantum states in a reservoir-engineered transmon chain
  W. Brzezicki, M. Silveri, M. Płodzień, F. Massel, and T. Hyart
  Phys. Rev. B 107, 115146 (2023)

• Quantum state purity versus average phonon number for characterization of mechanical oscillators in cavity optomechanics
  K. Børkje, F. Marin
  Phys. Rev. A 107, 013502 (2023)

Selected publications

• Backaction-evading measurement of entanglement in optomechanics
  F. Massel
  Phys. Rev. A 100, 023824 (2019)

• Heterodyne photodetection measurements on cavity optomechanical systems: Interpretation of sideband asymmetry and limits to a classical explanation,
  K. Børkje
  Phys. Rev. A 94, 043816 (2016)

• Position Measurements Obeying Momentum Conservation,
  P. Busch and L. Loveridge
  Phys. Rev. Lett. 106, 110406 (2011)

• Single-photon optomechanics,
  A. Nunnenkamp, K. Børkje, S.M. Girvin, Phys. Rev. Lett. 107, 063602 (2011)

• Stabilized entanglement of massive mechanical oscillators,
  C. F. Ockeloen-Korppi, E. Damskägg, J. M. Pirkkalainen, M. Asjad, A. A. Clerk, F. Massel, M. J. Woolley, M. A. Sillanpää, Nature 556, 478 (2018)

• Symmetry, Reference Frames and Relational Quantities in Quantum Mechanics,
  L. Loveridge, T. Miyadera and P. Busch. Found. Phys. 48, 2 (2018)