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SquiCS - Squeezed Quantum light in Communication and Sensing

SQuiCS develops squeezed light sources and quantum optical tools for precision sensing and secure communication. We work at the interface of nonlinear optics, integrated photonics and laser interferometry, with a particular focus on waveguide based and integrated photonic platforms.

Group leader

Vaishali Adya
Vaishali Adya assistant professor

At KTH, we work predominantly on squeezed light generation in waveguide systems and on the development and characterisation of waveguide based squeezed light sources for gravitational wave detection, biosensing and quantum communication. We also explore squeezed light as a resource for quantum key distribution and cascaded squeezed light sources for biosensing. Our current activities include prototyping of advanced control schemes for phase control of squeezed light generated in periodically poled LiNbO3 waveguides. We also develop all fiber frequency references that can be used for entanglement transfer, laser frequency and intensity noise stabalisation for experiments that need precise phase control such as twin field quantum key distribution and continuous variable quantum key distribution experiments that require squeezed light. We are also pursuing systematic modelling of waveguide based squeezers with realistic loss, phase noise and cascaded architectures to develop a feasibility matrix of experiments and requirements on squeezing platform.

Figure 1 Tomographic reconstruction of squeezing versus vaccum state

A second research direction explores quantum enhanced readout and cavity based squeezing schemes for precision metrology. This includes coupled cavity squeezing at normal mode splitting frequencies, quantum enhanced balanced heterodyne readout for differential interferometry, and loss resistant intracavity squeezing concepts, scatter light mitigation for future gravitational wave detectors. We are also interested in the practicality of quantum non-demolition experiments made possible with waveguide based nonlinear devices, use of machine learning for polarisation control and stabalisation and also wavelength tunable squeezed light sources.

The group works on technology development for the Einstein Telescope, LIGO, quantum teleportation experiments with the Australian National University, development of bright squeezed vacuum with Lund University, and is embedded in KTH’s broader quantum technology environment through WACQT and NQCIS. Current members of the group are Vaishali Adya (Group leader), Daniel Voigt (Postdoctoral fellow), Hilma Karlsson and Erik Svanberg (PhD students). We also have master students Linus Ekberg, Astrid Bergman, Daniela Kugler doing their master thesis with us. Stay tuned for how you can find their thesis!

Selected recent publications

  • E. A. T. Svanberg, D. Voigt, and V. Adya, Noise modelling of waveguide based squeezed light sources (arXiv, 2026). ( arXiv )
  • J. Junker et al., Squeezing at the Normal-Mode Splitting Frequency of a Nonlinear Coupled Cavity (Physical Review Letters, 2025). ( KTH )
  • D. W. Gould et al., Quantum Enhanced Balanced Heterodyne Readout for Differential Interferometry (Physical Review Letters, 2024). ( KTH )
  • H. Karlsson et al., All-fibre frequency reference for Twin-Field Quantum Key Distribution (CLEO/Europe-EQEC, 2025). ( Optica Publishing Group )
  • E. A. T. Svanberg et al., Quantum noise locking of squeezed light generated in periodically poled LiNbO3 waveguides (CLEO/Europe-EQEC, 2025). ( Optica Publishing Group )

Completed Thesis

  • Axel Segendorf, Bachelor thesis “Practical considerations for detection of squeezed light” ( link )
  • E. A. T. Svanberg, Master thesis “ Laser frequency stabilisation for twin-field quantum key distribution using a fiber-based Mach-Zehnder interferometer” ( link )

Outreach

Funding acknowledgment

Our research is supported by the Swedish Research Council (VR starting grant 2023-0519), Göran Gustafsson Prize for early career researchers and the Wallenberg Center for Quantum Technology (WACQT) in Sweden.