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.