# Quantum Fields Quantum Information Improved characterization of quantum

- Slides: 16

Quantum Fields & Quantum Information Improved characterization of quantum states for quantum information applications 2020 HUSKEY EXHIBITION Miller Eaton

Quantum Fields & Quantum Information “What do you mean by ‘State’? ? ” Classical State Quantum State YOU ARE HERE Atom - WHERE IS IT? - HOW MUCH ENERGY? … AND NOT IN MOTION 2 Light - WHAT COLOR? - WHERE IS IT GOING?

Quantum Fields & Quantum Information Where will you probably be? Probability to be seated “Oh crap! A talk on quantum physics!” 100% The talk starts 50% Sitting down for next talk 0% time Talk ends 3

Quantum Fields & Quantum Information Where is an atom? ? ? ? A C B 100% at B Prob. A 4 Spread out ‘Superposition’ Time passes… B Location C A B Location C

Quantum Fields & Quantum Information Where is an atom? ? ? ? A C B 100% at B Prob. Found it! Prob. A 5 Time passes… B Location C A B Location C

Quantum Fields & Quantum Information How does a superposition look? Wave interference – purely spatial 6 Complete descriptions require more – both position AND momentum (velocity) How would I actually measure this? ?

Quantum Fields & Quantum Information Mapping a Mountain 7

Quantum Fields & Quantum Information Mapping a Mountain 8

Quantum Fields & Quantum Information Reconstruction Computational inversion algorithms … Ø Commonly used to map quantum states, but… - Uses a lot of computer power - Results can be faulty 9

Quantum Fields & Quantum Information Direct Method Ø No computational algorithms needed, but… - Resolution limited by measuring single points - Cannot measure all quantum states with current technology 10

Quantum Fields & Quantum Information New Method - Overlap Unknown 11 Known Overlap Ø Taking several overlap measurements allows for quantum state reconstruction - Minimal computer resources needed - More types of states can be mapped with current technology - Results are guaranteed to be physical

Quantum Fields & Quantum Information Experimental Implementation Block/Unused Overlap Measurement Unknown state Repeat Calibrated input Result! 12 R. Nehra, M. Eaton, C. Gonzalez-Arciniegas, M. S. Kim, and O. Pfister, ar. Xiv preprint ar. Xiv: 1911. 00173. (2019)

Quantum Fields & Quantum Information This is useful!!! Detect Black Hole Collisions! Secret, un-hackable communication! Quantum Light 13 Quantum Computers!

Quantum Fields & Quantum Information Acknowledgements Quantum Fields and Quantum Information Group Department of Physics, University of Virginia

Quantum Fields & Quantum Information Loss Compensation Ø Tomographic process is lossy Ø Detector with non-unity efficiency Ø Lossy channel after state-prep Ø More generally, I can correct the entire density matrix 0 1 2 15 3 4 ? 0 1 2 3 4

Quantum Fields & Quantum Information (a) State Recovery after 50% loss: (b) Recovery including 2% intensity noise and 1 deg phase noise: 16 R. Nehra, M. Eaton, C. Gonzalez-Arciniegas, M. S. Kim, and O. Pfister, ar. Xiv preprint ar. Xiv: 1911. 00173. (2019)

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