Jonas Neergaard-Nielsen PRO
Associate Professor @ DTU Physics, Denmark
Distributed quantum sensing in a
continuous-variable entangled network
Xueshi Guo · Casper R. Breum · Shuro Izumi · Mikkel V. Larsen
Tobias Gehring · Jonas S. Neergaard-Nielsen · Ulrik L. Andersen
bigQ - Department of Physics, Technical University of Denmark
Johannes Borregaard · Matthias Christandl
QMATH - Department of Mathematical Science, University of Copenhagen
Task:
Simultaneously estimate multiple parameters - perhaps of spatially separated systems
Does entanglement help?
Yes!
- at least when estimating a global property.
First experimental demonstration
\phi_\mathrm{avg} = \frac{1}{M} \sum_{j=1}^{M}\phi_j
Example:
Average of multiple optical phase shifts
Small phase shifts:
Estimate with homodyne detection of phase quadrature
\langle \hat{P}_\mathrm{avg}\rangle \approx \sqrt{2\eta}\alpha \phi_\mathrm{avg}
\sigma_\mathrm{separable} = \frac{1}{2\sqrt{M}N\sqrt{1+\frac{1}{N}}}
\sigma_\mathrm{entangled} = \frac{1}{2MN\sqrt{1+\frac{1}{MN}}}
\sigma_\mathrm{SQL} = \frac{1}{2\sqrt{MN}}
Heisenberg scaling in probe energy and no. of sites/samples
Realistic (lossy) situation:
Heisenberg scaling disappears but sensitivity gain remains
Experiment
\sigma \equiv \frac{1}{SNR} = \frac{\sqrt{\langle\Delta \hat P^2_\mathrm{avg} \rangle}}{|\partial \langle \hat P_\mathrm{avg}\rangle /\partial\phi_\mathrm{avg}|}
Measured sensitivities
Casper R. Breum
Xueshi Guo
Casper R. Breum
Xueshi Guo
Mikkel V. Larsen
Mikkel V. Larsen
Johannes Borregaard
Distributed sensing
By Jonas Neergaard-Nielsen
