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 stable quantum behavior is usually masked by defects and impurities in the system. Indeed, a similarly-prepared time crystal was also observed in color-center impurities in solid diamond at Harvard.
- Ion Trap experiment (JQI/UMD): “Observation of a Discrete Time Crystal,” J. Zhang, P. W. Hess, A. Kyprianidis, P. Becker, A. Lee, J. Smith, G. Pagano, I.-D. Potirniche, A. C. Potter, A. Vishwanath, N. Y. Yao, C. Monroe, Nature 543, 217 (2017).
- Diamond experiment (Harvard): “Observation of discrete time-crystalline order in a disordered dipolar many-body system,” S. Choi, et al., Nature 543, 221 (2017).
- Nature news article on time crystals
- JQI News Release
It’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 98-99% 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.
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.
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.
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.
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.