Dr. Alexander V. Balatsky
Theoretical Division
Los Alamos National Laboratory
Mail Stop: B262
Los Alamos, New Mexico 87545

Title: Quantum Noise and Single Spin Detection
 
Abstract:
Recent scanning tunneling microscope (STM) experiments on magnetic centers on a surface demonstrate that one can get a spatially localized current signal  directly related  to a precessing spin. I will discuss possible  mechanisms that allows tunneling current couple to the spin degrees of freedom.  Important feature of these experiments is that signal is observed  in the  noise of the tunneling current . I  will argue that this experiment is another example, among many , of the noise spectroscopy.  Noise spectrocopy is a technique that allows one to extract spectroscopic information from the noise. As systems are getting smaller noise spectroscopy is a useful technique  to interrogate quantum systems [1]. 

A possible extension of this technique  where one  considers the  coupling between ac Josephson current and a  single spin in the junction is proposed [2].  I will argue that in an external magnetic field,  resulting in a  Larmor precession of a spin,  spin is nutating  at  Josehson frequency. Sidebands at sum and difference of Larmor and Josephson frequencies are formed.  Noise spectroscopy  is an emeregent  technique that might be applied  to surface magnetism studies and to quantum information. 
 
 
[1] S. Crooker, D. Rickel,  A.V. Balatsky and D. Smith,
"Spectroscopy of spontaneous spin noise as a probe of spin dynamics
and magnetic resonance", Nature  431,  p 49, (2004).
 
 [2] Jian-Xin Zhu, Z. Nussinov, A. Shnirman and A. V. Balatsky,
“Novel Spin Dynamics in a Josephson Junction",  PRL 92, 107001 (2004) ,
cond-mat/0306710.