Trapped Ions vs. Superconductors

figure1Connectivity between qubits in a quantum computer may be as important as clock speed and gate fidelity when it comes time to build large-scale quantum computers. We run several quantum algorithms on two 5-qubit programmable quantum computers: our fully-connected ion trap system, and the IBM Quantum Experience superconducting system.  The performance is seen to mirror the connectivity of the systems, with the ion trap system out-performing the superconducting system on all results, but particularly when the algorithm demands more connections.  This first comparison of algorithms on different platforms shows the power of having a programmable and reconfigurable system, which will be critical to successfully adapt to new quantum algorithms as they are discovered.

Observation of Time Crystals

In a delicate balance between strong interactions, weak disorder, and a periodic driving force, a collection of trapped ions qubits has been made to pulsate with a period that is relatively insensitive to the drive. This is a time crystal, where the stable pulsations emerge and break time symmetry – just like a freezing liquid breaks spatial symmetry and forms a spatial crystal. Trapped ion qubits don’t really need this added stability (they are nearly perfect on their own), but this observation may guide the stabilization of real-life solid systems, where true quantum behavior is usually masked by defects and impurities.

Reprogammable & Reconfigurable Quantum Computer

Cover 4 August 2016It’s just a five-qubit quantum computer, and anything it does is easily simulated on a laptop. However, these trapped ion qubits are fully connected, with entangling gates between all possible pairs. The qubits are dynamically “wired” from the outside with patterns of laser beams, so we can run any algorithm through software without modifying the base hardware.  While the individual gate operations are only about 98% pure, it should be possible to exceed the >99.9% purity others have demonstrated with two isolated ions. Most importantly, we have blueprints for scaling this system up to useful dimensions.

Many-body Localization with 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.

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.

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).