Spin detection

The authors found the neutral form of the polymer to be epr inactive. With increasing potential the number of spins detected increased from zero, reached a maximum and then decreased, as shown in Figures 3.79(a) and (b). The data were interpreted by the authors in terms of the initial formation of polarons followed by their subsequent recombination into bipolarons. 

The reactive intermediates mentioned above are initially ions and excited molecules and subsequently may be free radicals. Many ions are probably formed on irradiating PET, as judged by the large concentration of spins detected at —196°C. by electron spin resonance (ESR), but nothing is known directly about their chemical structure or reactivity. Any chemical role of excited molecules is equally a matter of conjecture. In these circumstances, the influence of dose rate will be discussed by reference to free radicals. Eventually, when more quantitative experimental data are obtained, the adequacy of free radical reactions may be better assessed, and the role of ions and excited molecules brought into perspective. 

These general remarks on the process of electron emission following photoionization lead us to a description of the experimental set-up used (spin-detection... 

Rugar, D., R. Budakian, H.J. Mamin, and B.W. Chui. 2004. Single spin detection by magnetic resonance force microscopy. Nature 430 329-332. 

Table 6.1 Unpaired Spins Detected in Deposited Film and Substrate After Glow Discharge Treatments for 1 Hour or Less at 30 W Power... 

Natural Spins Detected during the Solid-State Polymerization of 1,3-Butadiynes... 

Mamin HJ, Budakian R, Chui BW, Rugar D et al. (2005) Magnetic resonance force microscopy of nuclear spins Detection and manipulation of statistical polarization. Phys. Rev. B 72 24,413-24,419. 

Single spin detection by magnetic resonance force microscopy. 

Here, N is the number of qubit copies. To the scheme to work, this force must be comparable to the minimum force detectable by MRFM. For small polarization, the number of detectable qubits depends exponentially on p, just like in the liquid-state approach. However, for p 0.6 and above, there is a crossover from exponential to polynomial dependence ofnoap n l + p)/ l — p) (Figure 7.5). This is the main result of Ladd and co-workers proposal, for it means the system is scalable. Therefore, the usefulness of the scheme relies on the possibility to produce a large enough initial polarization, but there is no need of single spin detection and other difficulties present in the previous model. 

Single spin detection techniques solution for the sensitivity problem... 

In the previous section we have described some very ingenious proposals which, if implemented in practice, could lead to a large scale quantum information processor through NMR. It is important to emphasize that those proposals circumvent the scaling problem present in liquid-state NMR QIP experiments. However, whatever the sample architecture may be, it seems unavoidable the need to detect the NMR signal of very small spin concentrations. Ideally, single spin detection should be possible. Less than two decades ago, such a strict demand could sound hopeless conventional ESR needs a concentration of some... 

Figure 7.10 Single spin detection by MRFM. The result is from Rugar et al. (2004). The two plots correspond to different values of the external field. Changing the external field modifies the resonant slice, which in turn causes a shift in the peak. The average distance between spins in the sample is 300 A. Adapted with permission from [19].

C. Durkan, M.E. Welland, Electronic spin detection in molecules using scanning-tmmeling-microscopy-assisted electron-spin resonance, App. Phys. Lett. 80 (2002) 458. 

At these high dopant concentrations, the bipolarons, which are spinless, can become mobile under the application of an electrical field, thus giving rise to the high conductivity observed in CPs concomitant with absence of unpaired spins detectable by esr or other measurements. 

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