Chris Monroe, Rob Schoelkopf (Yale), and Misha Lukin (Harvard) write an article in the May 2016 issue of Scientific American about the necessity of modularity in building a quantum computer, with examples from leading physical systems of trapped ions, superconductors, and solid-state qubits.
“Many-body Localization” is an emergent quantum feature, where a system of disordered quantum particles does not thermalize even in the presence of strong interactions. MBL bestows some degree of quantum memory to an extended quantum system, even at high (or infinite) temperature where systems do not usually retain quantum coherence or entanglement. We observe the phenomenon of MBL in a controlled system of exactly 10 atoms with strong interactions and programmable disorder, bridging the chasm between controlled qubits and emergent features of condensed matter physics.
- “Many-Body Localization in a Quantum Simulator with Programmable Random Disorder,” Nature Physics doi:10.1038/nphys3783 (2016).
- JQI News release
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.
- “Realization of a Quantum Integer-Spin Chain with Controllable Interactions,” Phys. Rev. X 5, 021026 (2015)
- “Simulating the Haldane Phase in Trapped Ion Spins Using Optical Fields,” Phys. Rev. A 92, 012334 (2015).
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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.
- “Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System,” Science 345, 430 (2014).
- Supplementary Information
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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.
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.
- “Large Scale Modular Quantum Computer Architecture with Atomic Memory and Photonic Interconnects,” Phys. Rev. A 89, 022317 (2014). [AIP Synopsis]
- “Modular Entanglement of Atomic Qubits using Photons and Phonons,” Nature Physics 11, 37-42 (2015).
- “Quantum gates with phase stability over space and time,” Phys. Rev. A 90, 042316 (2014); “Entanglement of distinguishable quantum memories,” Phys. Rev. A 90, 040302(R) (2014).
- JQI News Release and Very cool animation of concept
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).