USIAS Fellows seminar: Creating, controlling and understanding complex quantum matter with ultracold atoms
By Shannon Whitlock, USIAS Fellow 2017
Quantum mechanics describes nature at the smallest of scales. It is also responsible for the collective behaviour of matter at low temperatures which often challenges our ‘classical’ intuition. In this regard, one of the most profound and paradoxical consequences of quantum mechanics is wave-particle duality; the notion that quantum objects simultaneously exhibit wave- and particle-like characteristics. While this rarely carries over to the behaviour of everyday objects, two of the greatest physics discoveries of the 20th century – superconductivity, the spectacular and sudden disappearance of electrical resistance, and superfluidity, the frictionless flow of liquids below a critical temperature – are both macroscopic manifestations the collective wavelike behaviour of many particles in the same quantum state. Similarly, quantum collective phenomena can give rise to totally new optical and electronic properties of materials or can enhance how charge, energy or information is transported in complex molecules and quantum devices. However, apart from a few very special cases, it is not possible to predict how these desirable properties come about from the underlying microscopic physics and it is not clear if such effects can be engineered deliberately.
In recent years, tremendous progress has been made in creating and controlling quantum systems, all the way down to the level of individual particles such as single atoms and photons. In the Exotic Quantum Matter Laboratory we use laser cooling and trapping to isolate the atoms from their environment and to cool them to nearly absolute zero temperature (−273.15 °C), at which point that their behaviour is almost entirely governed by quantum mechanical principles. From there we excite the atoms to highly excited states (Rydberg states) to introduce and control their microscopic interactions. In this way we can engineer synthetic quantum systems in which we can manipulate the underlying quantum ‘rules’ and watch how complex quantum systems evolve in an exceptionally clean setting.
Compared to conventional materials, quantum systems made of ultracold atoms have the advantage that the microscopic physics can be known precisely and key macroscopic observables can be directly accessed by experiment. As a result, they can be used as ‘quantum simulators’ to gain insight into how complex quantum behaviour emerges from simple interactions between many particles. They also offer an ideal playground to explore exotic quantum behaviour such as superconductivity, superfluidity, magnetism and non-equilibrium quantum dynamics, with wide ranging applications, e.g., helping to answer how quantum coherence influences molecular dynamics responsible for the remarkably efficient conversion of light into energy in photosynthetic systems, and inspiring new architectures for computation which harness quantum effects to solve problems far beyond the capabilities of current computing schemes.
