Quantum Simulation of Spin Chains

SPIN-1        Three-level systems are useful as “qutrits” in quantum information processing with more storage capacity than qubits, but they can also represent effective “spin-1″ particles that have interesting magnetic properties.  We have encoded qutrits in three levels of 171Yb+ ions, and engineered Ising and XY magnetic interactions between several ions to entangle and prepare complex ground states of this system.  Future work will study certain topological phases that emerge from this many body spin-1 system.Spin1

MANY BODY SPECTROSCOPY        It is computationally intractable to calculate the spectrum of energy levels in a lattice of spins fully-connected through Ising or XY magnetic interactions.  We have developed a new technique akin to MRI that images particular energy levels of a spin chain encoded in an array of trapped ions, by modulating a transverse magnetic field and directly observing the resulting spin configuration.spectroscopy-latest-01


QUANTUM “LIGHT CONES” OF ENTANGLEMENT PROPAGATION        We have measured dynamics of the propagation of quantum information through a many body spin chain connected by long-range Ising or XY magnetic interactions, and observe that the “speed limit” of this propagation can break bounds associated with conventional local interactions, first described by Lieb and Robinson in 1972.

Modular Entanglement of Atoms

Gallery image 1 Monroe PRA 2014-V1

Modularity is everywhere, from social networks and transportation hubs to biological function. Modular systems are always necessary for mitigating complexity, especially in computer systems where the latest processors have up to 256 modular cores.  We propose a realistic modular quantum computing design that is scalable to huge numbers of qubits, while resistant to errors. Entanglement within a module is afforded through local phonon interactions, which can be extended to other qubit modules through photonic interfaces. Experimentally, we report the first step in such an architecture by entangling remote ions in different ion traps while also showing local entanglement between ions in a single ion trap module as a demonstration of both photon and phonon buses in a single network.  The entanglement rate between modules is nearly 10/sec, orders of magnitude faster than previous results, and much faster than the observed decoherence rate, thus representing the first demonstration of a scalable quantum network in any photonic platform.  Moreover, we show how to phase-lock gates over space and time between multiple modules, a crucial prerequisite for scalability.  We finally show that even if the photons from different modules have different optical frequencies, entanglement fidelity of the linked quantum memories can be recovered, without sacrificing entanglement rate, by feed-forwarding timing information on the coincidence interference.

Optimized and Fast Quantum Gates between Many Trapped Ions

Trapped ion qubits are conventionally entangled through a single collective mode of motion coupled by the Coulomb interaction.  In order to entangle ions immersed in a large collection, resolving a single motional mode poses a serious slowdown as the number of ion qubits increases.  We circumvent this limitation by using optimally shaped pulses of light that couple to all modes of motion. We apply these optimally-shaped gates to entangle various pairs of qubits in a 5-ion collection, and also demonstrate that such shaped gates can be less sensitive to errors.


Ultrafast Spin-Motion Entanglement and Interferometry with a Single Atom

Entanglement in a Flash from JQI News on Vimeo.

The lab’s ultrafa$t team has generated quantum entanglement between a single atom’s motion and its spin state thousands of times faster than previously reported, demonstrating unprecedented control of atomic motion. This work, which may lead to faster and better quantum computer logic gates, is described a recent issue of Physical Review Letters.

This experiment focuses on using highly energetic laser pulses to perform qubit operations. Previously, they set a record for the fastest spin flip in these systems: a mere 50 picoseconds. Here they continue their work by blasting the ion so strongly that the qubit quickly becomes linked to its motion. Such speedy operations are more typically associated with solid state systems such as electrons in semiconductors or superconductors. Here the speed of operations combined with the pristine quantum environment of atoms provide the best of both worlds. READ more @ JQI website

“Ultrafast Spin-Motion Entanglement and Interferometry with a Single Atom,” J. Mizrahi, C. Senko, B. Neyenhuis, K.G. Johnson, W.C. Campbell, C.W.S. Conover, C. Monroe, Physical Review Letters, 103, 203001 (2013)

Scaling the Ion Trap Quantum Information Processor

201303_science_coverRecently Science Magazine invited JQI fellow Chris Monroe and Duke Professor Jungsang Kim to speculate on ion trap technology as a scalable option for quantum information processing. The article is highlighted on the cover of the March 8, 2013 issue of Science, which is dedicated to quantum information. The cover portrays a photograph of a surface trap that was fabricated by Sandia National Labs and used to trap ions at JQI and Duke, among other laboratories. Read more at JQI’s website.


Paramagnetic to Ferromagnetic phase transition with N=16 trapped ion spins (two qubytes)

field lines art8 no 16 ionAFM different ions-stretch-01-blue yellow and white ion-004

Frustration, or the competition between interacting components of a network, is often responsible for the complexity of many body systems, from social and neural networks to protein folding and magnetism. In quantum magnetic systems, frustration arises naturally from competing spin-spin interactions given by the geometry of the spin lattice or by the presence of long-range antiferromagnetic couplings. Frustrated magnetism is a hallmark of poorly understood systems such as quantum spin liquids, spin glasses and spin ices, whose ground states are massively degenerate and can carry high degrees of quantum entanglement. The controlled study of frustrated magnetism in materials is hampered by short dynamical time scales and the presence of impurities, while numerical modeling is generally intractable when dealing with dynamics beyond N~30 particles. Alternatively, a quantum simulator can be exploited to directly engineer prescribed frustrated interactions between controlled quantum systems, and several small-scale experiments have moved in this direction. In this article, we perform a quantum simulation of a long-range antiferromagnetic quantum Ising model with a transverse field, on a crystal of up to N = 16 trapped Yb+ atoms. We directly control the amount of frustration by continuously tuning the range of interaction and directly measure spin correlation functions and their dynamics through spatially-resolved spin detection. We find a pronounced dependence of the magnetic order on the amount of frustration, and extract signatures of quantum coherence in the resulting phases.

“Emergence and Frustration of Magnetism with Variable-Range Interactions in a Quantum Simulator,” R. Islam, C. Senko, W.C. Campbell, S. Korenblit, J. Smith, A. Lee, E.E. Edwards, J.C.C. Wang, J.K. Freericks, C. Monroe, Science, 340, 583 (2013)