Quantum information with cold atoms and non-classical light
http://hdl.handle.net/2117/23888
2020-11-30T08:57:51ZLoophole-free Bell inequality violation using electron spins separated by 1.3 kilometres
http://hdl.handle.net/2117/79298
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres
Hensen, B.; Bernien, H.; Dréau, A. E.; Reiserer, A.; Kalb, N.; Blok, M. S.; Ruitenberg, J.; Vermeulen, R. F. L.; Schouten, R. N.; Abellán, Carlos, 1990-; Amaya, W.; Pruneri, P.; Mitchell, Morgan W.; Markham, M.; Twitchen, D. J.; Elkouss, D.; Wehner, S.; Taminiau, T. H.; Hanson, R.
More than 50 years ago1, John Bell proved that no theory of nature that obeys locality and realism2 can reproduce all the predictions of quantum theory: in any local-realist theory, the correlations between outcomes of measurements on distant particles satisfy an inequality that can be violated if the particles are entangled. Numerous Bell inequality tests have been reported3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in ‘loopholes’13, 14, 15, 16. Here we report a Bell experiment that is free of any such additional assumption and thus directly tests the principles underlying Bell’s inequality. We use an event-ready scheme17, 18, 19 that enables the generation of robust entanglement between distant electron spins (estimated state fidelity of 0.92 ± 0.03). Efficient spin read-out avoids the fair-sampling assumption (detection loophole14, 15), while the use of fast random-basis selection and spin read-out combined with a spatial separation of 1.3 kilometres ensure the required locality conditions13. We performed 245 trials that tested the CHSH–Bell inequality20 S ≤ 2 and found S = 2.42 ± 0.20 (where S quantifies the correlation between measurement outcomes). A null-hypothesis test yields a probability of at most P = 0.039 that a local-realist model for space-like separated sites could produce data with a violation at least as large as we observe, even when allowing for memory16, 21 in the devices. Our data hence imply statistically significant rejection of the local-realist null hypothesis. This conclusion may be further consolidated in future experiments; for instance, reaching a value of P = 0.001 would require approximately 700 trials for an observed S = 2.4. With improvements, our experiment could be used for testing less-conventional theories, and for implementing device-independent quantum-secure communication22 and randomness certification23, 24.
2015-11-16T11:47:07ZHensen, B.Bernien, H.Dréau, A. E.Reiserer, A.Kalb, N.Blok, M. S.Ruitenberg, J.Vermeulen, R. F. L.Schouten, R. N.Abellán, Carlos, 1990-Amaya, W.Pruneri, P.Mitchell, Morgan W.Markham, M.Twitchen, D. J.Elkouss, D.Wehner, S.Taminiau, T. H.Hanson, R.More than 50 years ago1, John Bell proved that no theory of nature that obeys locality and realism2 can reproduce all the predictions of quantum theory: in any local-realist theory, the correlations between outcomes of measurements on distant particles satisfy an inequality that can be violated if the particles are entangled. Numerous Bell inequality tests have been reported3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in ‘loopholes’13, 14, 15, 16. Here we report a Bell experiment that is free of any such additional assumption and thus directly tests the principles underlying Bell’s inequality. We use an event-ready scheme17, 18, 19 that enables the generation of robust entanglement between distant electron spins (estimated state fidelity of 0.92 ± 0.03). Efficient spin read-out avoids the fair-sampling assumption (detection loophole14, 15), while the use of fast random-basis selection and spin read-out combined with a spatial separation of 1.3 kilometres ensure the required locality conditions13. We performed 245 trials that tested the CHSH–Bell inequality20 S ≤ 2 and found S = 2.42 ± 0.20 (where S quantifies the correlation between measurement outcomes). A null-hypothesis test yields a probability of at most P = 0.039 that a local-realist model for space-like separated sites could produce data with a violation at least as large as we observe, even when allowing for memory16, 21 in the devices. Our data hence imply statistically significant rejection of the local-realist null hypothesis. This conclusion may be further consolidated in future experiments; for instance, reaching a value of P = 0.001 would require approximately 700 trials for an observed S = 2.4. With improvements, our experiment could be used for testing less-conventional theories, and for implementing device-independent quantum-secure communication22 and randomness certification23, 24.Long-term laser frequency stabilization using fiber interferometers
http://hdl.handle.net/2117/78831
Long-term laser frequency stabilization using fiber interferometers
Kong, Jia; Lucivero, Vito Giovanni; Jiménez-Martínez, Ricardo; Mitchell, Morgan W.
We report long-term laser frequency stabilization using only the target laser and a pair of 5 m fiber interferometers, one as a frequency reference and the second as a sensitive thermometer to stabilize the frequency reference. When used to stabilize a distributed feedback laser at 795 nm, the frequency Allan deviation at 1000 s drops from 5.6 × 10−8 to 6.9 × 10−10. The performance equals that of an offset lock employing a second, atom-stabilized laser in the temperature control.
2015-11-05T14:48:27ZKong, JiaLucivero, Vito GiovanniJiménez-Martínez, RicardoMitchell, Morgan W.We report long-term laser frequency stabilization using only the target laser and a pair of 5 m fiber interferometers, one as a frequency reference and the second as a sensitive thermometer to stabilize the frequency reference. When used to stabilize a distributed feedback laser at 795 nm, the frequency Allan deviation at 1000 s drops from 5.6 × 10−8 to 6.9 × 10−10. The performance equals that of an offset lock employing a second, atom-stabilized laser in the temperature control.Passive Decoy-State Quantum Key Distribution with Coherent Light
http://hdl.handle.net/2117/78820
Passive Decoy-State Quantum Key Distribution with Coherent Light
Curty, Marcos; Jofre, Marc; Pruneri, Valerio; Mitchell, Morgan W.
Signal state preparation in quantum key distribution schemes can be realized using either an active or a passive source. Passive sources might be valuable in some scenarios; for instance, in those experimental setups operating at high transmission rates, since no externally driven element is required. Typical passive transmitters involve parametric down-conversion. More recently, it has been shown that phase-randomized coherent pulses also allow passive generation of decoy states and Bennett–Brassard 1984 (BB84) polarization signals, though the combination of both setups in a single passive source is cumbersome. In this paper, we present a complete passive transmitter that prepares decoy-state BB84 signals using coherent light. Our method employs sum-frequency generation together with linear optical components and classical photodetectors. In the asymptotic limit of an infinite long experiment, the resulting secret key rate (per pulse) is comparable to the one delivered by an active decoy-state BB84 setup with an infinite number of decoy settings.
2015-11-05T12:20:59ZCurty, MarcosJofre, MarcPruneri, ValerioMitchell, Morgan W.Signal state preparation in quantum key distribution schemes can be realized using either an active or a passive source. Passive sources might be valuable in some scenarios; for instance, in those experimental setups operating at high transmission rates, since no externally driven element is required. Typical passive transmitters involve parametric down-conversion. More recently, it has been shown that phase-randomized coherent pulses also allow passive generation of decoy states and Bennett–Brassard 1984 (BB84) polarization signals, though the combination of both setups in a single passive source is cumbersome. In this paper, we present a complete passive transmitter that prepares decoy-state BB84 signals using coherent light. Our method employs sum-frequency generation together with linear optical components and classical photodetectors. In the asymptotic limit of an infinite long experiment, the resulting secret key rate (per pulse) is comparable to the one delivered by an active decoy-state BB84 setup with an infinite number of decoy settings.Macroscopic Quantum State Analyzed Particle by Particle
http://hdl.handle.net/2117/27115
Macroscopic Quantum State Analyzed Particle by Particle
Beduini, Federica A.; Zielińska, Joanna Ada; Lucivero, Vito G.; Icaza Astiz, Yannick A. de; Mitchell, Morgan W.
Macroscopic quantum phenomena, e.g., superconductivity and squeezing, are believed to result from
entanglement of macroscopic numbers of particles. We report the first direct study of this kind of
entanglement: we use discrete quantum tomography to reconstruct the joint quantum state of photon pairs
extracted from polarization-squeezed light. Our observations confirm several predictions from spinsqueezing
theory [Beduini et al., Phys. Rev. Lett. 111, 143601 (2013)], including strong entanglement and
entanglement of all photon pairs within the squeezing coherence time. This photon-by-photon analysis may
give insight into other macroscopic many-body systems, e.g., photon Bose-Einstein condensates.
2015-03-30T14:04:18ZBeduini, Federica A.Zielińska, Joanna AdaLucivero, Vito G.Icaza Astiz, Yannick A. deMitchell, Morgan W.Macroscopic quantum phenomena, e.g., superconductivity and squeezing, are believed to result from
entanglement of macroscopic numbers of particles. We report the first direct study of this kind of
entanglement: we use discrete quantum tomography to reconstruct the joint quantum state of photon pairs
extracted from polarization-squeezed light. Our observations confirm several predictions from spinsqueezing
theory [Beduini et al., Phys. Rev. Lett. 111, 143601 (2013)], including strong entanglement and
entanglement of all photon pairs within the squeezing coherence time. This photon-by-photon analysis may
give insight into other macroscopic many-body systems, e.g., photon Bose-Einstein condensates.Strong experimental guarantees in ultrafast quantum random number generation
http://hdl.handle.net/2117/26741
Strong experimental guarantees in ultrafast quantum random number generation
Mitchell, Morgan W; Abellán, Carlos, 1990-; Amaya, Waldimar
We describe a methodology and standard of proof for experimental claims of quantum random-number
generation (QRNG), analogous to well-established methods from precision measurement. For appropriately
constructed physical implementations, lower bounds on the quantum contribution to the average min-entropy can
be derived from measurements on the QRNG output. Given these bounds, randomness extractors allow generation
of nearly perfect “-random” bit streams. An analysis of experimental uncertainties then gives experimentally
derived confidence levels on the randomness of these sequences. We demonstrate the methodology by
application to phase-diffusion QRNG, driven by spontaneous emission as a trusted randomness source. All
other factors, including classical phase noise, amplitude fluctuations, digitization errors, and correlations due to
finite detection bandwidth, are treated with paranoid caution, i.e., assuming the worst possible behaviors consistent
with observations. A data-constrained numerical optimization of the distribution of untrusted parameters is used
to lower bound the average min-entropy. Under this paranoid analysis, the QRNG remains efficient, generating
at least 2.3 quantum random bits per symbol with 8-bit digitization and at least 0.83 quantum random bits per
symbol with binary digitization at a c
2015-03-16T16:22:53ZMitchell, Morgan WAbellán, Carlos, 1990-Amaya, WaldimarWe describe a methodology and standard of proof for experimental claims of quantum random-number
generation (QRNG), analogous to well-established methods from precision measurement. For appropriately
constructed physical implementations, lower bounds on the quantum contribution to the average min-entropy can
be derived from measurements on the QRNG output. Given these bounds, randomness extractors allow generation
of nearly perfect “-random” bit streams. An analysis of experimental uncertainties then gives experimentally
derived confidence levels on the randomness of these sequences. We demonstrate the methodology by
application to phase-diffusion QRNG, driven by spontaneous emission as a trusted randomness source. All
other factors, including classical phase noise, amplitude fluctuations, digitization errors, and correlations due to
finite detection bandwidth, are treated with paranoid caution, i.e., assuming the worst possible behaviors consistent
with observations. A data-constrained numerical optimization of the distribution of untrusted parameters is used
to lower bound the average min-entropy. Under this paranoid analysis, the QRNG remains efficient, generating
at least 2.3 quantum random bits per symbol with 8-bit digitization and at least 0.83 quantum random bits per
symbol with binary digitization at a c