Characterizing and understanding coherent many-body effects in complex quantum systems remains one of the frontiers in condensed-matter and statistical physics research. Experimental advances from quantum control and simulation are being combined with theoretical insights from quantum information theory to shed new light on these questions. Our group currently explores questions in many-body physics using two experimental platforms.
Central Spin Dynamics of Phosphorus Dopants in Silicon
The 4.2% abundant 29Si spins are the dominant source of electron spin echo decays in lightly-doped natural silicon samples at and below 4 K. The spin dynamics of the isolated donor spin are determined by its hyperfine interactions with surrounding nuclear spins (an instance of the classic central spin problem). Many-body magnetic dipolar interactions between the nuclear spins induce a fluctuating nuclear magnetic field at the site of the donor electron spin causing the echo decay. While the physics of this system has been explored extensively at 300 mT and seemed well understood, our recent experiments at 8.4 T (at the National High Magnetic Field Laboratory) have yielded surprising new results. The decays – which are expected to be field-independent – are shorter at high magnetic fields, and increase in the presence of low power optical excitation! We are currently developing a theoretical model to explain these observations.
Dynamics of 3D dipolar-coupled systems
It has been suggested that the long-time dynamical behavior of a non-integrable, interacting, closed quantum system should exhibit one of two characteristic behaviors – either thermalize and loses memory of its initial state as (a consequence of the eigenstate thermalization hypothesis); or localize in a many-body localized phase that retains memory of the original state. Understanding how this happens has important fundamental implications for quantum statistical physics and practical implications for quantum technologies. One dimensional spin systems give us access to integrable models – such as the z-kicked chain above – whose dynamics can be analytically calculated.
It is as yet unclear how the interplay between disorder and interaction strength influences the dynamics of 3D spin systems – especially those that have anisotropic interactions whose sign varies with angle. In solid state NMR experiments we can generate multiple quantum coherences that are a particular form of out-of-time ordered correlator. Our experiments can generate very high MQC orders.