News from the Mitchell Group

2016/07/08 Spinor Condensate

Ultracold atoms team creates a magnetic superfluid. When bosonic atoms like rubidium-87 get sufficiently cold, the form a new phase of matter that is both superfluid (no friction at all) and ferromagnetic.

2016/05/24 Ehrenfest Award

Group Leader Morgan Mitchell awarded the Ehrenfest Award for Foundations of Physics. Congratulations, Morgan !

2016/05/13 New low-noise detector for atomic quantum control

2016/05/02 Squeezed-light spin noise spectroscopy

2015/12/16 Three articles in special Bell test issue of PRL

Three back-to-back articles (250401, 250402, 250403) and cover of special issue on loophole-free Bell tests.

2015/11/12 How to test Macrorealism with macroscopic objects

Article in Physical Review Letters shows how quantum non-demolition measurements can be used to test Leggett and Garg's ideas of macroscopic realism in macroscopic systems.

2015/10/29 Nature paper on loophole-free Bell test

Loophole-free Bell test contradicts local realism. Article in Nature. Reporting in New York Times, The Economist, The Times of London.

2015/04/17 new doctor: Naeimeh Behbood

Dr. Naeimeh Behbood graduated with the thesis Generation of Macroscopic Spin Singlets in Cold Atomic Ensembles. Congratulations, Naeimeh !

2015/3/27 Squeezed State Analyzed Particle by Particle

Article in PRL shows that suqeezed beams of light consist of entangled photons.

March 2015 A macroscopic quantum state analyzed particle by particle

Article in PRL We observe for the first time the entanglement of microscopic particles (in our case photons) inside of a macroscopic quantum state (in our case squeezed light). Featured in Science News.

2015/01/27 new doctor: Yannick Alan de Icaza Astiz

Dr. Yannick Alan de Icaza Astiz graduated with a thesis in Optimal Signal Recovery for Pulsed Balanced Detection. Congratulations, Yannick !

August 2014 Generation of macroscopic singlet states

Article in PRL By applying quantum non-demolition measurements to an unpolarized atomic ensemble, we generate a macroscopic singlet state. At least 500,000 atoms become entangled in the process. Editor's suggestion in PRL Featured in Scientific American.

July 2014 Distinguished visitor: Ferran Adrià

Ferran Adrià

Ferran Adrià visits the lab, talks about creativity and very cold atoms.

June 2014 Ultrasensitive Atomic Spin Measurements with a Nonlinear Interferometer

Article in PRX We demonstrate that for some measurements, e.g. measuring atomic spin alignment, a nonlinear measurement beats the best possible "ordinary" measurement. This confirms a proposal by Sergio Boixo and Carlton Caves, and is beyond the standard models of quantum sensitivity limits. Editor's choice in Science.

June 2014 New group member

Ricardo Jimenez MartinezRicardo joins us from NIST Boulder.

March 2014 Distinguished visitor: Steven Chu

Steven Chu

Steven Chu (Nobel 1997) visits the lab, talks about atom interferometry, climate change, and re-creating the culture of Bell Labs.

2014/02/07 new doctor: Mario Napolitano

Mario Napolitano successfully defended his dissertation Interaction-based nonlinear quantum metrology with a cold atomic ensemble. Congratulations, Mario !

2014/02/10 New group member

Jia Kong

Jia Kong (visiting PhD student) joins from East China Normal University (Shanghai).

January 2014 Record speed in quantum randomness generation

Article in Optics Express

We demonstrate 43 gigabits per second randomness generation, using off-the-shelf components. In collaboration with V. Pruneri's group at ICFO. Newspaper report in El Periodico

Fall 2013 Visitor Lukas Slodicka

Lukas Slodicka?Lukas joins us from Innsbruck before moving on to Olomouc.

Fall 2013 Visitor Ricardo Jimenez

Ricardo Jimenez MartinezRicardo joins us from NIST Boulder.

May 2013 Quantum non-demolition measurement of a macroscopic material system

Jan 2013 Ultra-gentle measurements using quantum entanglement

Dec 2012 Sensitivity beyond the projection-noise limit by spin squeezing

2012/12/07 New group member

Natali Martinez

Natalie Martinez (post-doc) joins from Los Alamos National Labs (USA).

2012/11/27 new doctor: Brice Dubost

Brice Dubost successfully defended his dissertation Light-Matter Interaction with Atomic Ensembles. Congratulations, Brice !

2012/06/29 new doctor: Florian Wolfgramm

Florian Wolfrgamm successfully defended his dissertation Atomic Quantum Metrology with Narrowband Entangled and Squeezed States of Light. Congratulations, Florian !

Vanguard of Science award for Morgan and Mario

Morgan and Mario honored for work on quantum metrology. Here they are receiving the award "Vanguardia de la Ciencia." Ceremony presided over by Andreu Mas-Colell, conseller de Economia i Coneixement (at right). Article in La Vanguardia (in Spanish)

New group members

Thomas Vanderbruggen? Joanna Zielinska

Thomas Vanderbruggen (post-doc) joins from the Institut d'Optique in France, and Joanna Zielinska (PhD), joins from Warsaw, Poland.

New group members

Silvana Palacios Ferran Martin

Silvana Palacios (PhD) joins from the Universidad Nacional Autonoma de Mexico, and Ferran Martin (PhD), joins from the Universitat Autonoma de Barcelona.

Mitchell Group awarded a prestigious European Research Council Starting Grant

The project, "Atomic Quantum Metrology," will test revolutionary new proposals in ultra-sensitive measurement using quantum optics.

Morgan becomes ICREA Professor

Morgan has been selected to join the prestigious Catalan research organization ICREA (Institució Catala de Reçerca i Estudis Avancats).

New group member

Silvana PalaciosSilvana, from the UNAM (Mexico), joins the group as a Master student.

New group members

Pau Gómez Kabelka Joanna Zielinska

Pau Gomez Kabelka, from Barcelona and Joanna Zielinska, from Torun, Poland join the group for the summer.

Interaction-based quantum metrology showing scaling beyond the Heisenberg limit

Editor's summary:
Quantum metrology uses entanglement and other quantum resources to improve precision measurement, resulting in sensitivity limited by the Heisenberg uncertainty principle. But in theory, interactions among particles may allow scaling beyond this limit into 'super-Heisenberg' territory. Napolitano et al. prove experimentally that this can indeed occur in a nonlinear, non-destructive measurement of the magnetization of an atomic ensemble. The work shows that inter-particle interactions could be a useful resource for quantum metrology, although the relative performance of nonlinear versus linear measurements has yet to be explored more generally Nature 471, 486–489 (2011). A collection of press is here.

High resolution magnetic vector-field imaging with cold atomic ensembles

We present a magnetic field imaging technique based on spatially resolved detection of Larmor precession. An optically trapped, elongated, and cold atomic sample of rubidium serves as magnetic field probe. We detect Larmor precession with a spatial and a temporal resolution of ∼ 50 μm and ∼ 120 μs, respectively. Projection-noise limited absorption imaging, feasible with current technologies, implies a sensitivity of ∼ 10 pT/Hz1/2 at 50 μm resolution; addition of an optical lattice could give ∼ 300 fT/Hz1/2 sensitivity. Appl. Phys. Lett. 98, 074101 (2011)

Atom-Resonant Heralded Single Photons by Interaction-Free Measurement

We demonstrate the generation of rubidium-resonant heralded single photons for quantum memories. Photon pairs are created by cavity-enhanced down-conversion and narrowed in bandwidth to 7 MHz with a novel atom-based filter operating by “interaction-free measurement” principles. At least 94% of the heralded photons are atom-resonant as demonstrated by a direct absorption measurement with rubidium vapor. A heralded autocorrelation measurement shows gc(2)(0)=0.040±0.012, i.e., suppression of multiphoton contributions by a factor of 25 relative to a coherent state. The generated heralded photons can readily be used in quantum memories and quantum networks. PRL, 106, 053602 (2011)

New group members

Prof. Nicolas Godbout from Polytechnique Montréal (CA) joins the group for a 3 month visiting period and Giorgio Colangelo, previously at Università di Pisa (IT), starts his PhD in the atom lab.


We organize a workshop on 'Quantum Technology with Atomic Ensembles' inviting the tribunal members of Marco Koschorreck's PhD defense, to present some of their recent researches.

EMALI Conference

We host the ''International Meeting on Engineering, Manipulation and Characterization of Quantum States of Matter and Light.'' Top researchers from 11 countries participate. quantumoptics.es/EMALI2010

Nonlinear Quantum Metrology

We describe nonlinear quantum

atom–light interfaces and nonlinear quantum metrology in the collective continuous variable formalism. We develop a nonlinear effective Hamiltonian in terms of spin and polarization collective variables and show that model Hamiltonians of interest for nonlinear quantum metrology can be produced in 87Rb ensembles. With these Hamiltonians, metrologically relevant atomic properties, e.g. the collective spin, can be measured better than the 'Heisenberg limit' ?1/N, where N is the number of photons. In contrast to other proposed nonlinear metrology systems, the atom–light interface allows both linear and nonlinear estimation of the same atomic quantities. New J. Phys. 12 093016 (2010)

Quantum Non-Demolition Measurements of Atomic Spin

Something about the QND expt. Phys. Rev. Lett. 105, 093602 (2010)

Squeezed-Light Optical Magnetometry

]] We demonstrate a

light-shot-noise-limited magnetometer based on the Faraday effect in a hot unpolarized ensemble of rubidium atoms. By using off-resonant, polarization-squeezed probe light, we improve the sensitivity of the magnetometer by 3.2 dB. The technique could improve the sensitivity of the most advanced magnetometers and quantum nondemolition measurements of atomic spin ensembles. Phys. Rev. Lett. 105, 053601 (2010)

Sub-Projection-Noise Sensitivity in Broadband Atomic Magnetometry

We demonstrate

sub-projection-noise sensitivity of a broadband atomic magnetometer using quantum nondemolition spin measurements. A cold, dipole-trapped sample of rubidium atoms provides a long- lived spin system in a nonmagnetic environment, and is probed nondestructively by paramagnetic Faraday rotation. The calibration procedure employs as known reference state, the maximum-entropy or ‘‘thermal’’ spin state, and quantitative imaging-based atom counting to identify electronic, quantum, and technical noise in both the probe and spin system. The measurement achieves a sensitivity 1.6 dB (2.8 dB) better than projection-noise (thermal state quantum noise) and will enable squeezing-enhanced broadband magnetometry. Phys. Rev. Lett. 104, 093602 (2010)