Anomalies in the NMR of Silicon: Unexpected Spin Echoes in a Dilute Dipolar Solid

TL;DR

This paper reports unexpected and unexplained phenomena in NMR spin echo measurements of silicon, revealing new challenges and insights for solid state physics and quantum computation involving long-range interactions.

Contribution

It uncovers novel, unexplained anomalies in silicon NMR echoes, highlighting potential implications for quantum systems with long-range qubit interactions.

Findings

Observation of long tails and even-odd asymmetry in echo trains

Detection of anomalous stimulated echoes with peculiar characteristics

Results challenge existing explanations in solid state NMR

Abstract

NMR spin echo measurements of $^{29}$Si in Silicon powders have uncovered a variety of surprising phenomena that appear to be independent of doping. These surprises include long tails and even-odd asymmetry in Carr-Purcell-Meiboom-Gill (CPMG) echo trains, and anomalous stimulated echoes with several peculiar characteristics. Given the simplicity of this spin system, these results, which to date defy explanation, present a new and interesting puzzle in solid state NMR. In the broader context of quantum computation, these experiments suggest that similar surprises may be found in other systems with small, long-range, qubit-qubit interactions, particularly when ``bang-bang'' control is used.