ForschungTopical Groups
Sub-standard quantum limit in suspended interferometers

Sub-standard quantum limit in suspended interferometers

Probing the limits imposed on precision interferometry with suspended macroscopic mirrors by the quantum nature of light and aim to surpass them.


This topical group operates a 10-metre prototype interferometer facility located in the institute for gravitational physics. The 10-m prototype offers an environment with extremely low displacement noise, a large volume in ultra-high vacuum, a highly stable laser with a power of 35 watts, a very stable DC supply network, comprehensive detection of environmental influences, fully digital control infrastructure and sufficient flexibility to quickly change the experimental setup - if necessary.

The first and most important experiment being set up in this facility is a Michelson interferometer, which explores the interferometric standard quantum limit (SQL). To achieve the SQL, the interferometer sensitivity must be limited only by the quantum noise at the measurement frequency. The SQL can be surpassed by exploiting correlations between the amplitude and phase quantum fluctuations of the light inside the interferometer. Different approaches for surpassing the SQL will be tested and analysed.


  • low noise mirror suspensions
  • seismic isolation systems (active/passive)
  • low noise actuators
  • precision interferometry
  • shot noise limited photodiodes
  • laser stabilisation (amplitude/frequency)
  • optical scattering of mirrors
  • vacuum out-gassing test chamber
  • microscopical investigation of surfaces
  • in vacuum seismically isolated platforms


Brown DD, Jones P, Rowlinson S, Leavey S, Green AC, Töyrä D et al. PYKAT: Python package for modelling precision optical interferometers. SoftwareX. 2020 Jul 1;12. 100613.


Kirchhoff R, Mow-Lowry CM, Bergmann G, Hanke MM, Koch P, Köhlenbeck SM et al. Local active isolation of the AEI-SAS for the AEI 10 m prototype facility. Classical and quantum gravity. 2020 Mai 4;37(11). 115004.


Koch P, Cole GD, Deutsch C, Follman D, Heu P, Kinley-Hanlon M et al. Thickness uniformity measurements and damage threshold tests of large-area GaAs/AlGaAs crystalline coatings for precision interferometry. Optics express. 2019 Dez 9;27(25):36731-36740.


Involved QF Members
Members Institution Relevant Expertise
David Wu, LeaderAEISub-Standard Quantum Limit Interferometry
Harald LückAEINext Generation Gravitational Wave Observatories; Sub-Standard Quantum Limit Interferometry
Matteo CarlassaraAEICommissioning of the SQL Interferometer
Michèle HeursAEIBackaction-Evading Techniques
Benno WillkeAEISqueezed Light Sources; Advanced Light Sources
Philip KochAEIoptics, suspensions
Johannes LehmannAEImirror suspensions
Juliane von WrangelAEIfibre welding, bonding
Janis WöhlerAEIthermal noise interferometer
Henning VahlbruchAEISqueezed states of light
Sara al KershiAEIMirror suspensions