Quantum Information

Winter 2015 | jila.colorado.edu Winter 2015 | jila.colorado.edu &MATTER QUANTUM Entanglement p.3 JILA Light & Matter The 2nd Annual Poster Fest was held on October 3, 2014. JILA supports an eclectic and innovative research community. The Poster Fest provides an opportunity for JILA scientists to learn about the research of other JILAns and present information about their own work. JILA Light & Matter is published quarterly by the Scientific Communications Office at JILA, a joint institute of the University of Colorado Boulder and the National Institute of Standards and Technology. The editors do their best to track down recently published journal articles and great research photos and graphics. If you have an image or a recent paper you’d like to see featured, contact us at: [email protected]. Please check out this issue of JILA Light & Matter online at https://jila.colorado.edu/publications/jila/ light-matter Julie Phillips, Science Writer Kristin Conrad, Design & Production Steven Burrows, Art & Photography Gwen Dickinson, Editor Winter 2015 | jila.colorado.edu Stories Atoms, Atoms, Frozen Tight 1 Quantum Entanglement 3 Exciting Adventures in Coupling 7 The Polarized Express 13 Mutant Chronicles 15 The Quantum Identity Crisis 17 Features In the News 5 th JILA Tower 10 Floor Renovation 5 The JILA Science Crossword 9 Amelia Earhart Day 11 How Did They Get Here? 19 Atomic & Molecular Physics Atoms, Atoms, Frozen Tight in the Crystals of the Light, What Immortal Hand or Eye Could Frame Thy Fearful Symmetry? —after William Blake ymmetries described by SU(N) group theory made it possible for physicists in the 1950s to This first-ever spectroscopic Sexplain how quarks combine to make protons observation of SU(N) orbital and neutrons and JILA theorists in 2013 to model the behavior of atoms inside a laser. Now, the Ye magnetism in 87Sr atoms group has observed a manifestation of SU(N≤10) symmetry in the magnetic behavior of strontium-87 cooled to micro-Kelvin (87Sr) atoms trapped in crystals of light created by intersecting laser beams inside a quantum simula- temperatures was reported tor (originally developed as an optical atomic clock). online in Science Express on This first-ever spectroscopic observation of SU(N) August 21, 2014. orbital magnetism in 87Sr atoms cooled to micro- Kelvin temperatures was reported online in Science have predicted that a chiral spin liquid will form if Express on August 21, 2014. 87Sr atoms are prepared in all 10 nuclear spin states and cooled down in a two-dimensional lattice Several advances made this observation possible: (crystal of light). This exotic substance has no appar- (1) seminal theory work by the Rey group predict- ent order even at ultralow temperatures approach- ed the magnetic behavior of 87Sr atoms at cold ing absolute zero! and ultracold temperatures, (2) exquisite measurement precision available from an ultrastable laser The researchers responsible for launching this developed for the 87Sr-lattice optical atomic clock, new, exciting work include research associate Xibo (3) the ability to freeze out the motional states of Zhang, graduate students Mike Bishof and Sarah the atoms, but preserve the flow of information, at Bromley, research associate Christina Krauss and relatively “high” μK temperatures, (4) the use of 87Sr Professor Peter Zoller of the University of Innsbruck atoms, whose 10 nuclear spin states are decoupled (Austria), Professor Marianna Safronova of the from their interparticle interactions, and (5) the ex- University of Delaware, and Fellows Ana Maria Rey perimental control of the number of 87Sr atoms in and Jun Ye. the ground and excited electronic states used as orbitals. For a more whimsical description of the science in this highlight, please see Alice’s Adventures in This groundbreaking work opens the door to: (1) Quantum Land: Lost inside a strontium-lattice watch, precision studies of collisions between nearly iden- at https://jila.colorado.edu/book/alices-adventures- tical 87Sr atoms that differ only in the states of their quantumland/01. ✺ nuclear spins, (2) a deeper understanding of the role of atomic orbitals in collisions and chemical X. Zhang, M. Bishof, S. L. Bromley, C. V. Kraus, M. S. Safronova, P. Zoller, reactions, and (3) investigations of quantum mag- A. M. Rey, J. Ye, Science 345, 1467–1473 (2014). netism and exotic materials. For instance, theorists 1 Winter 2015 , JILA Light & Matter Strontium atoms in a quantum simulator display SU(N≤10) symmetry because of having 10 different nuclear spin states that are decoupled from their electronic and motional states. This symmetry was predicted by the Rey group and recently observed by the Ye group. Credit: The Ye and Rey groups, and Steve Burrows, JILA Winter 2015 . JILA Light & Matter 2 The use of laser light in an optical cavity improves precision measurement by reducing the quantum fuzziness of 500,000 Rb atoms by a factor of 10. In the process, the laser light entangles hundreds of the atoms. Credit: The Thompson group and Steve Burrows, JILA 3 Winter 2015 , JILA Light & Matter Quantum Information Quantum EntanglementEntanglement Coming Soon to a Precision Measurement Near You he spooky quantum property of entanglement is set to become a powerful tool in precision measurement, thanks to researchers in the Thompson Tgroup. Entanglement means that the quantum states of something physical—two atoms, two hundred atoms, or two million atoms—interact and retain a connection, even over long distances. Even without exploiting entanglement, atoms are more noise in the length has no bearing on a mea- already used as exquisite sensors of time, gravity, surement of time. rotations, and magnetic fields because the rules of quantum mechanics allow them to be prepared in The reason squeezing works is because the identical states. However, this matching comes at Thompson group’s measurement of quantum a price. Even individual identical atoms are funda- fuzziness entangles the atoms. In a large entan- mentally fuzzy because of how things work in the gled state, the fuzziness of each individual atom quantum world. It’s as though the hands of your is partially cancelled by the fuzziness of other clock were blurry, making it difficult to precisely atoms. As a result, the overall fuzziness of all tell the time. What’s worse, no amount of squint- the entangled atoms is reduced. So, if precision ing makes this quantum blurriness go away. measurement specialists entangle independent atoms, there are clever ways to make them work What the Thompson group has done is to figure out together. And when they work together, they can how to create the right kind of “eyes” to measure become a clock with higher precision than would the quantum fuzziness in 500,000 rubidium (Rb) be possible if all the atoms were separately trying atoms and reduce it by a factor of 10. This exciting to measure the exact time (as well as length, or result was the largest directly observed measure- another physical quantity). ment enhancement due to entanglement ever reported for atoms. It appeared online in Nature The Thompson group was able to make an entan- Photonics on July 13, 2014. The research team re- gled collection of atoms by allowing all the atoms sponsible for this work included recently minted to interact with the same laser light many times by Ph.D. Justin Bohnet, graduate students Kevin Cox, bouncing the light back and forth between mirrors Matt Norcia, and Josh Weiner, recent JILA grad prior to measuring the orientation of the clock Zilong Chen, and Fellow James K. Thompson. arrows, or atomic spins. The information carried by the laser light told the researchers about the One way to think about this experiment is quantum state of all of the atoms, but without that a measurement “squeezes” the quantum telling them the quantum state of any single atom. noise. Squeezing means that the researchers That’s because very little light with information were able to design the measurement technique about the state of individual atoms comes out to preferentially force quantum noise out of the sideways from the laser cavity. The strategy of width of their quantum clock hand and into its just measuring the state of all the atoms allowed length instead. A narrower clock hand allows one every atom to remain in a quantum superposition to read the clock more precisely. At the same time, of both pointing up and down simultaneously. Winter 2015 , JILA Light & Matter 4 Quantum Information | News Keeping the atoms in this state was the key to gen- erating entanglement. In the News In the quantum world, measurements are usually associated with destroying entanglement. But, A selection of news, awards, and what now the Thompson group has shown that the right is happening around JILA type of measurement can actually produce large amounts of entanglement. JILA Leadership Changes Per JILA’s organizational charter, JILA Fellows are nomi- “This was the first time anyone has actually gone in nated to serve two-year terms as JILA Chair and Co- and directly observed a factor of 10 improvement Chair. At the end of December, 2014, Murray Holland over the original quantum fuzziness of atoms,” said stepped down as JILA Chair after a busy term and Thompson. “This is a lot of entanglement. And, it Deborah Jin became the JILA Chair for the 2015–2017 is what we actually see without correcting for any term. Dana Anderson takes Deborah Jin’s place as the imperfections in the experiment. We also think that new JILA Associate Chair. we can build even better eyes in the future to gen- erate even more entanglement.” New Clock May End Time As We Know It (NPR) From National Public Radio, November 3, 2014: Thompson predicts that this new work means that entangled states will soon be coming to a preci- At the nearby University of Colorado Boulder [Ye Lab] sion measurement near you.

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