Closing loopholes in Bell tests of local realism

Transcription

1 Mx lnck Institute of Quntum Optics MQ Grching / Munich Germny Closing loopholes in Bell tests of locl relism Johnnes Kofler Workshop Quntum hysics nd the Nture of Relity Interntionl Acdemy Trunkirchen Austri Novemer 03

2 Overview Assumptions in Bell s theorem Relism Loclity Freedom of choice Closing loopholes Loclity Freedom of choice Fir smpling Coincidence time Conclusion nd outlook

3 Acknowledgements Se Woo Nm Mriss Giustin Bernhrd Wittmnn Sven Rmelow Rupert Ursin Anton Zeilinger Jn-Åke Lrsson

4 History Quntum mechnics nd hidden vriles 97 Kopenhgen interprettion Bohr Heisenerg etc. 93 Von Neumnn s wrong proof of nonpossiility of hidden vriles 935 Einstein-odolsky-Rosen prdox 95 De Broglie-Bohm nonlocl hidden vrile theory 964 Bell s theorem on locl hidden vriles 97 First successful Bell test Freedmn & Cluser Bohr nd Einstein 95

5 Locl relism Clssicl world view: Relism: hysicl properties re proilisticlly defined prior to nd independent of mesurement Loclity: No physicl influence cn propgte fster thn the speed of light Externl world ssive oservers

6 Bell s Assumptions Bell s ssumptions Relism: Hidden vriles determine glol pro. distri.: pa A A λ Loclity: OI Outcome independence: pa Bλ = pa λ & vice vers for B SI Setting independence: pa λ = pa λ & vice vers for B fctorizility: pab λ = pa λ pb λ 3 Freedom of choice: ρ λ = ρ ρλ = ρλ J. F. Cluser nd A. Shimony Rep. rog. hys J. S. Bell hysics J. S. Bell Spekle nd Unspekle in Quntum Mechnics p

7 Bell s Assumptions Bell s theorem Relism + Loclity + Freedom of choice + X Bell s inequlity Bell s originl derivtion only implicitly ssumed freedom of choice: explicitly: ABλ BAλ loclity freedom of choice implicitly: ρλ Aλ Bλ ρλ c Aλ Bcλ Remrks: originl Bell pper : X = erfect nti-correltion CHSH : X = Fir smpling J. S. Bell hysics J. F. Cluser M. A. Horne A. Shimony R. A. Holt RL

8 Loopholes Loopholes: mintin locl relism despite exp. Bell violtion Why importnt? quntum foundtions security of entnglement-sed quntum cryptogrphy Three min loopholes: Loclity loophole hidden communiction etween the prties closed for photons Freedom-of-choice loophole settings re correlted with hidden vriles closed for photons 00 3 Fir-smpling detection loophole mesured suensemle is not representtive closed for toms 00 4 superconducting quits nd for photons 03 6 E λ A. Aspect et l. RL G. Weihs et l. RL T. Scheidl et l. NAS M. A. Rowe et l. Nture M. Ansmnn et l. Nture M. Giustin et l. Nture

9 Loclity & freedom of choice Tenerife B L lm EA E λ L lm Tenerife Loclity: A is spce-like sep. from nd B B is spce-like sep. from nd A pab λ = pa λ pb λ Freedom of choice: nd re rndom nd re spce-like sep. from E λ p λ = p T. Scheidl R. Ursin J. K. T. Herst L. Rtschcher X. M S. Rmelow T. Jennewein A. Zeilinger NAS

10 Fir-smpling loophole Fir smpling: Unfir smpling: Locl detection efficiency depends only on hidden vrile: η A = η A λ η B = η B λ oserved outcomes fithfully reproduce the sttistics of ll emitted prticles Locl detection efficiency is setting-dependent η A = η A λ η B = η B λ fir-smpling detection loophole Locl relistic models 3 A λ = sign λ B λ = sign λ 4 : 9 ηa λ = λ ηb λ = 4 : ηa λ = ηb λ = λ 9 : η λ 0 η λ 0 9 A = B = dλ E = ηa ηb S π Reproduces the quntum predictions of the singlet stte with detection efficiency /3 Detection efficiency is not optionl in security-relted tsks device-independent quntum cryptogrphy: fked Bell violtions 4 A B =. M. erle RD F. Selleri nd A. Zeilinger Found. hys N. Gisin nd B. Gisin hys. Lett. A I. Gerhrdt Q. Liu A. Lms-Linres J. Skr V. Scrni V. Mkrov C. Kurtsiefer RL

11 CHSH vs. CH/Eerhrd inequlity CHSH inequlity two detectors per side correltion functions fir-smpling ssumption used in derivtion requires indep. verific. of η tot > 8.8 % mximlly entngled sttes optiml J. F. Cluser M. A. Horne A. Shimony R. A. Holt RL A. Grg nd N. D. Mermin RD CH 3 Eerhrd 3 inequlity only one detector per side proilities counts no fir-smpling ssumption in the derivtion no requirement to mesure η tot impossile to violte unless η tot > 66.7 % non-mx. entngled sttes optiml + + E E E E 3 J. F. Cluser nd M. A. Horne RD H. Eerhrd RA

12 Trnsition-edge sensors Working principle Superconductor 00 nm thick tungsten film t 00 mk t trnsition edge Superconducting trnsition-edge sensors Steep dependence of resistivity on temperture Mesurle temperture chnge y single sored photon Chrcteristics High efficiency > 95 % Low noise < 0 Hz hoton-numer resolving icture from: Topics in Applied hysics A. E. Lit A. J. Miller S. W. Nm Opt. Express

13 Setup Sgnc-type entngled pir source Non-mx. entngled sttes ψ + r HV r VH r = + Fier-coupling efficiency > 90% Filters: ckgroundphoton elimintion > 99% M. Giustin A. Mech S. Rmelow B. Wittmnn J. K. J. Beyer A. Lit B. Clkins T. Gerrits S. W. Nm R. Ursin A. Zeilinger Nture

14 Experimentl results M. Giustin A. Mech S. Rmelow B. Wittmnn J. K. J. Beyer A. Lit B. Clkins T. Gerrits S. W. Nm R. Ursin A. Zeilinger Nture J. K. S. Rmelow M. Giustin A. Zeilinger rxiv: [qunt-ph] 03 0 : Eerhrd = S S C C C C J B A hoton: only system for which ll min loopholes re now closed not yet simultneously Violtion of Eerhrd s inequlity 300 seconds per setting comintion Collection efficiency η tot 75% No ckground correction etc. C C C C S A S B J Exp. dt Model Devition 004 % 00 % 0 % 5 % 04 % 043 % 0 : CH + + +

15 The coincidence-time loophole Fir coincidences: Unfir coincidences: Locl detection time depends only on hidden vrile: T A = T A λ T B = T B λ identified pirs fithfully reproduce the sttistics of ll detected pirs Detection time is setting-dependent T A = T A λ T B = T B λ coincidence-time loophole Locl relistic model: Stndrd moving windows technique: coincidence if T A λ T B λ ½τ coincidences re missed CH/Eerhrd violted C + C C + S A C + S B 0 J.-Å. Lrsson nd R. Gill EL

16 Closing the coincidence-time loophole Moving windows coincidence-time loophole open redefined fixed locl time slots coincidence-time loophole closed c Triple window for coinc. coincidence-time loophole closed J.-Å. Lrsson M. Giustin J. K. B. Wittmnn R. Ursin S. Rmelow rxiv:

17 Appliction to experimentl dt Eerhrd inequ. J = C C C + C + S + S A B 0 Triple-window method coinc.-time loophole closed Fixed time slots coinc.-time loophole closed Moving windows coinc.-time loophole open simultneous closure of fir-smpling detection nd coincidence-time loophole J.-Å. Lrsson M. Giustin J. K. B. Wittmnn R. Ursin nd S. Rmelow rxiv:

18 Conclusion nd outlook Loophole: How to close: Loclity Freedom of choice spce-like seprte A & B nd B & A rndom spce-like seprte E & rndom Fir smpling use CHSH nd lso show η > 8.8% detection or use CH/Eerhrd C + C C + S A C + S B 0 Coincidencetime use fixed time slots or window-sum method hotons: ech of the loopholes hs een closed leit in seprte experiments Loophole-free experiment still missing ut in rech

19 Loopholes hrd/impossile to close Futher loopholes: Superdeterminism: Wit-t-the-source: Wit-t-the setting: Common cuse for E nd E is further in the pst; pirs wit efore they strt trvelling futher in the pst; photons used for the setting choice wit efore they strt trveling Wit-t-the-detector: AB re frther in the future photons wit efore detection collpse loclity loophole E λ Actions into the pst