Sunday, June 25, 2017

Multiparameter estimation with single photons

Chenglong You, Sushovit Adhikari, Yuxi Chi, Margarite L. LaBorde, Corey T. Matyas, Chenyu Zhang, Zuen Su, Tim Byrnes, Chaoyang Lu, Jonathan P. Dowling, Jonathan P. Olson
It was suggested in Ref. [Phys. Rev. Lett. 114, 170802] that optical networks with relatively inexpensive overhead---single photon Fock states, passive optical elements, and single photon detection---can show significant improvements over classical strategies for single-parameter estimation, when the number of modes in the network is small (n < 7). A similar case was made in Ref. [Phys. Rev. Lett. 111, 070403] for multi-parameter estimation, where measurement is instead made using photon-number resolving detectors. In this paper, we analytically compute the quantum Cram\'er-Rao bound to show these networks can have a constant-factor quantum advantage in multi-parameter estimation for even large number of modes. Additionally, we provide a simplified measurement scheme using only single-photon (on-off) detectors that is capable of approximately obtaining this sensitivity for a small number of modes.
Comments: 13 pages, 3 figures
Subjects: Quantum Physics (quant-ph)
Cite as: arXiv:1706.05492 [quant-ph]
  (or arXiv:1706.05492v1 [quant-ph] for this version)

Friday, June 23, 2017


My last day at QICT@NICT! A couple of new traditions this year. Thursday night do-it-yourself Korean-style BBQ dinner and Friday sushi lunch to welcome all the visitors. Final meeting with Kouichi Semba, Masahiro Takeoka, and Masahide Sasake with my students Haoyu Qi and Zhihao Xiao in about an hour to iron out the theory of a superconducting qubit strongly coupled to the quantum photon field in a microwave cavity. 

Dr. Semba's team is vigorously working on the experiments and we're happy to help with the theory. 

Semba-san's superconducting qubit
in the the super-duper ultra-strong coupling regime.

Haoyu and Masahiro are making great progress on a squeezing assisted quantum cryptography scheme. More photos of writing on the white board, the Korean BBQ, and sushi lunch!

Then tomorrow I catch my 10AM flight from Tokyo back home: NRT-DFW-BTR! Apparently I escaped running into tropical storm Cindy on the way back. 

Me making mistakes.

Haoyu fixing my mistakes!

Traditional photo of me in front of some random piece of equipment:
In this case the free-space laser communication system.
Traditional Japanese-style Korean BBQ.
I'm doing my Popeye imitation.

"To past, present, and future collaborations!" 
LSU PhD student Haoyu Qi gives his speech.

LSU PhD student Zhihao Xiao gives his.

Saturday, June 17, 2017


Then end of week one at NICT. Lots of progress on many fronts! Publications are coming soon. Week exciting for other reasons. First publication on exciting data from Chinese Quantum Satellite. Read my interview in Newsweek here

After so much fine work my two students, Haoyu Qi and Zihao Xiao, celebrated with our Japanese colleagues with seafood, beer, and a wee drop of saké. 


Wednesday, June 14, 2017

#WIDOMSUMVAC — Tokyo Day Four!

Signed off on a Memorandum of Understanding to codify collaborations between the Japanese NICT Quantum ICT Advanced Development Center and the LSU Hearne Institute of Theoretical Physics.

Group picture of QICT and me! Dr. Masahide Sasaki, Distinguished Researcher to my immediate left,
Dr. Koichi Semba, to his left (in back), Director Dr. Masahiro Takeoka to his left.
My students and I had great discussion with Dr. Semba and his researchers, as well as with Dr. Takeuchi, on their latest experiments with superconducting qubits coupled to a micro resonator in the ultrastrong coupling regime. This ain't your grandma's Jaynes-Cummings model. 

Free space laser cryptography system. Not in use today due to rain.

Always something fun to see on the walk to NICT from the train station.
Star Wars Memorabilia takes over the tea room.

Monday, June 12, 2017


I have now been in the Tokyo airport three times in three weeks! Returned again last night to visit Drs. Masahide Sasaki and Masahiro Takeoka and their colleagues at the Quantum ICT Advanced Development Center, at the Japan National Institute of Information and Communications Technology (NICT). My two LSU PhD students, Haoyu Qi and Zhihao Xiao, are already here about mid-way through their eight-week summer research collaboration. It was good to catch up on old work and new work and today we began hammering out the research plan for the next two weeks I am here. QICT has a very close integration with theory and experiment and I'm looking forward to learning a lot and expanding our current collaboration which is now formalized by a Memorandum of Understanding. 

Come to LSU to do your PhD in our Quantum Science and Technologies group and can get to spend your summer in Shanghai, Tokyo, or Los Angeles near the beach!

Discussions today ranged over entanglement assisted channel capacities using two-mode squeezed vacuum, as well as tomography on superconducting qubits coupled to an LC circuit. 

After a 12 hour flight I relax with sushi, wine, and Japanese soap operas.

Colonel Sanders always greets me on my trips here.

Dr. Yoshiaki Tsujimoto explains the downconversion experiment.

Debate rages over the potential applications.

Wednesday, June 7, 2017


After the Dean's office requested I post my summer adventures in a blog, I'd focused on not being at LSU for the past three weeks, but I'm back this week to meet all of the summer students and make mid-course corrections on their projects.
QST Meeting at LSU!
The projects include:

The Return of Quantum Atomic Clock Synchronization!

Catching the Wave of the Quantum Internet!

This Ain't Your Grandma's Squeezed Vacuum!

Room-Temperature Photon-Number-Resolving Detection Without Room-Temperature Photon-Number-Resolving Detectors!

Super-Duper Resolution!

What the Heck is Written on the Board!?

In addition to the left-behind PhD students who are not away this summer we have summer undergrads; Osa Adun, David Lawrence, Kenji Arai, Corey Matyas, Samara Levy, Tony Mirasola, and High School Students; Mary Catherine Lorio, Deepti Vaidyanathan, and Jefferson Koonce, funded under the NSF REU program and the US Army AEOP programs. 

Friday, June 2, 2017


Wonderful discussions and new physics ideas at OIST. Friday I had a chance to hear from the theory students in the group of Thomas Busch! Many experimental puzzles, many theoretical solutions, and all is very exciting. I look forward to return for two weeks in April!

Group photo of the AMO experimentalists and friends.

The aftermath.

Who invented the pushme-pullyou trap?

Finally. Theorists!

Theory selfie.

Sasha has too many levels.

Kind of a Hibachi place.

Tritium, center, is radioactive.

They don't throw the food at you.

Thomas appears surpised.

Sile seems dubious.

A minute later it grabbed my face and implanted me with an alien.

Okay. Who left torpedos in the parking lot again.

Vanilla Air is very Plane.

Wednesday, May 31, 2017


After the somewhat grueling 24-hour flight from Baton Rouge to Okinawa, I arrived late Tuesday night local time. Given that I had just spent two weeks in Shanghai, which is only an hour different than here, I'm not jet lagged! Having missed dinner all together Tuesday evening, I raced down to the OIST cafeteria for breakfast Wednesday morning, which consisted of three slices of pizza, a boiled egg, a glass of orange juice, and a double-shot latte. I may not be regular again until the next Clinton administration.

At 9AM sharp Prof. Síle Nic Chormaic's postdoc, Dr. Jinjin Du, gave us a short tour of the local part of the island and then we had lab tours and discussions from 11AM until about 12:30PM, another break for pizza and coffee, and then back for more discussion on the transfer of higher-order modes of light through fibers to couple nonlinearly with neutral atoms — does LSU have a theory for that!

The Prof. Irina Novikova, my long-time collaborator gave the experimental version of our collaboration in a nice seminar on the generation of multimode squeezed light in rubidium vapor. 

I will give the theory version of our collaboration tomorrow in a not so nice seminar. Next Síle (pronounced "Shelia" will be taking us out for local cuisine — Italian / Spanish / French food with local ingredients. Then tomorrow we do it all over again! 

My lovely little cottage on a cliff.

View from my back porch.
What have you done with my pet bottle, Cecil!?

A used TOKAMAK that doubles as a tunnel?
Eggxactly what the doctor ordered?
OIST on approach.

OIST koi pond.

Left to right: Alexandre Akoulchine, Irina Novikova, JinJin Du.
"You can't take a photo of a hole — it is an absence of matter!"
A relic from 1947?

I can't define a photon, but I know one when I see one.

Laser-cooled Rubidium atoms interact with an optical fiber.

OIST PhD Student, Thomas Nieddu, explains why it is all very "cool".

Irina regales us with tales of experiments for multimode squeezed light

View from my office.