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As an initial demonstration of harnessing spin fluctuations, we created a hyperpolar-ized spin state by selectively capturing and storing the especially large statistical fluctuations. To do this, we continuously monitor the spin signal and wait until a fluctuation exceeds a predetermined threshold value

Dfhreshold (19). Upon registering a suitable fluctuation, the microwave power is turned off at a maximum of the cantilever motion, which leaves the instantaneous spin polarization pointing along B0. In the absence of the microwave field, the spins no longer respond to the cantilever motion, and the nonequilibrium state of the spin ensemble can be stored in the laboratory frame for as long as a spin-lattice relaxation time, Tr The stored magnetization can then be read out by reapplying the microwave field at a maximum of the cantilever motion and using the standard interrupted OSCAR (iOSCAR) protocol.

The average of 2800 individual capture-store-readout sequences, taken with use of setup 2, is shown (Fig. 3). For the data in Fig. 3A, the captured magnetization was stored for 1 s in the laboratory frame (i.e., with the microwave field off) and then read out with use of the iOSCAR protocol. The readout signal had a peak amplitude of 9.4 mHz, which we estimate corresponds to an average magnetization of mstored = 5.5mB. When the storage time was increased to 5 s (Fig. 3B), the peak stored magnetization decreased by 14% to mstored = 4.8mB. This drop in m^red is the result of depolarization due to longi tudinal relaxation, indicating Tx ~ 30 s. The observed T1 includes the contribution from the lattice as well as tip-induced relaxation (11).

In addition to simply selecting and capturing desired fluctuations, we can also take a more active approach by applying realtime feedback to the spin system in order to continuously guide its evolution. As a demonstration of feedback control, we have rectified the spin fluctuations by monitoring the spin signal and applying a p inversion to the entire spin ensemble whenever Df < 0 (19). The p inversions, accomplished with the use of adiabatic inversion, flip the sign of the spin imbalance so as to always keep Dm positive in the iOSCAR reference frame. Figure 4A shows a 200-s record of the iOSCAR signal, taken with the use of setup 1, along with vertical bars indicating times when p inversions were applied. In contrast to Fig. 2B, the histogram of the signal with feedback control (Fig. 4B, solid curve) now shows a nonzero mean value of 5.6 mHz corresponding to ~7.0|jb. Thus, through the use of feedback, we have essentially hyper-polarized the spins in the rotating frame of the iOSCAR measurement. This spin order can once again be transferred to the laboratory frame, stored, and then read out (Fig. 4, C and D).

We have demonstrated real-time control of electron spins in small ensembles using two spin manipulation protocols: fluctuation capture and fluctuation rectification. Because the present single-shot detection sensitivity is already approaching the single spin level, relatively modest improvements in detection signal-to-noise ratio should allow real-time quantum state detection and control of individual electron spins.

References and Notes

1. J. C. Maxwell, Theory of Heat (Longmans, London, ed. 6, 1880).

5. H. J. Mamin, R. Budakian, B. W. Chui, D. Rugar, Phys. Rev. Lett. 91, 207604 (2003).

6. D. Rugar, R. Budakian, H. J. Mamin, B. W. Chui, Nature 430, 329 (2004).

7. G. P. Berman, V. N. Gorshkov, D. Rugar, V. I. Tsifrinovich, Phys. Rev. B 68, 094402 (2003).

8. B. W. Chui et al., in Technical Digest of the 12th International Conference on Solid-State Sensors and Actuators (Transducers '03), IEEE, Boston, MA, 8 to 12 June 2003 (IEEE, Piscataway, NJ, 2003), pp. 1120-1123.

9. D. Mozyrsky, I. Martin, D. Pelekhov, P. C. Hammel, Appl. Phys. Lett. 82, 1278 (2003).

10. J. G. Castle, D. W. Feldman, P. G. Klemens, R. A. Weeks, Phys. Rev. 130, 577 (1963).

11. B. C. Stipe etal., Phys. Rev. Lett. 87, 277602 (2001).

12. T. R. Albrecht, P. Grutter, D. Horne, D. Rugar, J. Appl. Phys. 69, 668 (1991).

13. G. P. Berman, D. I. Kamenev, V. I. Tsifrinovich, Phys. Rev. A 66, 023405 (2002).

14. C. P. Slichter, Principles of Magnetic Resonance (SpringerVerlag, Heidelberg, ed. 3, 1996).

15. G. P. Berman, F. Borgonovi, H. S. Goan, S. A. Gurvitz, V. I. Tsifrinovich, Phys. Rev. B 67, 094425 (2003).

16. T. A. Brun, H. S. Goan, Phys. Rev. A 68, 032301 (2003).

17. H. Gassmann, M. S. Choi, H. Yi, C. Bruder, Phys. Rev. B 69, 115419 (2004).

18. For measurement setups 1 and 2, we estimate the average magnitude of the lateral gradient to be ~1.7 x 105 T m-1.

19. Materials and methods are available as supporting material on Science Online.

20. We thank J. Sidles, K. Holczer, and A. Hero for discussions and D. Pearson and M. Sherwood for technical assistance. This work was supported by the Defense Advanced Research Projects Agency Three-

Dimensional Atomic-Scale Imaging program administered through the U.S. Army Research Office.

Supporting Online Material

www.sciencemag.org/cgi/content/full/307/5708/408/ DC1

Materials and Methods Figs. S1 and S2 References

25 October 2004; accepted 15 December 2004 10.1126/science.1106718

M2W, respectively) by a deep, beheaded, flat-floored paleovalley that is truncated by the fault and flanked by well-defined lateral moraines (Fig. 2). The crest of the lateral moraine east of the paleovalley is well preserved, and its eastern edge extends to the base of the faceted range front. There is no catchment on the mountain slope facing this valley, indicating that it must correspond to a former channel of the Manikala glacier (Fig. 2 and fig. S3). The youngest moraine group, M1 (Fig. 2), is the only one present on both sides of the Manikala outwash valley and displays well-preserved terminal lobes and sharply defined ridge crests.

Upstream from the fault, the limits of glacial incision reach the base of the triangular facets that border the Manikala valley. Downstream, the M1 and M2E moraine ridge crests extend linearly to the fault and, when realigned with the sharp edge of glacial bedrock incision south of the fault, provide the only piercing points accurate enough to obtain offset estimates (14) (Fig. 2 and fig. S4). Once restored from satellite images, the M1 and M2E offsets are 220 ± 10 m and 1520 ± 50 m, respectively. Another moraine complex with morphologically similar surfaces and offsets is found at the terminus of the Tajiang Daer glacial valley ~10 km to the west (fig. S3), lending additional support to this reconstruction (fig. S4).

10Be model ages for samples collected along the moraine ridge crests (Fig. 2B) define consistent age clusters that can be used to date their abandonment (15). Ages on the two M2 ridges (Fig. 3) fall mostly between 103 and 204 thousand years (ky) (15 samples; mean age, 152 ± 28 ky), with a subset of seven samples between 132 and 150 ky old (mean age, 140 ± 5.5 ky). Samples WG-3, WG-4, and WG-7, on the eastern moraine (M2E), are more than 55 ky older than the main M2E population (132 to 150 ky old). We consider these three samples to be outliers, probably originating from more ancient till upstream. Examination of the M2 population with the outliers excluded reveals two distinct subgroups: a younger cluster of nine samples with ages of 103 to 149 ky (mean age, 133 ± 15 ky) and an older group of six samples of 160 to 204 ky (mean age, 181 ± 14 ky). The nine samples from the M1 moraine yield a younger mean age of 35 ± 9 ky. Seven samples fall between 36 and 45 ky (mean age, 40 ± 3 ky), and two distinctly younger samples have ages of 21 ± 1.0 ky.

Slip-Rate Measurements on the Karakorum Fault May Imply Secular Variations in Fault Motion

M.-L. Chevalier,1,2 F. J. Ryerson,2* P. Tapponnier,1 R. C. Finkel,2 J. Van Der Woerd,3 Li Haibing,4 Liu Qing5

Beryllium-10 surface exposure dating of offset moraines on one branch of the Karakorum Fault west of the Gar basin yields a long-term (140- to 20-thousand-year) right-lateral slip rate of ~10.7 ± 0.7 millimeters per year. This rate is 10 times larger than that inferred from recent InSAR analyses (~1 ± 3 millimeters per year) that span ~8 years and sample all branches of the fault. The difference in slip-rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales. Such fluctuations would be consistent with mechanical coupling between the seismogenic, brittle-creep, and ductile shear sections of faults that reach deep into the crust.

The Karakorum Fault in Tibet is the main Quaternary right-lateral fault north of the Himalayas. Determining its past and present motion is critical to understanding the kinematics of Asian continental deformation and the rheology of the continental lithosphere (1, 2). The fault trends roughly parallel to the western Himalayan range, extending from at least Kailas to the Pamirs, a length of >1200 km (Fig. 1). Its Quaternary slip rate remains poorly constrained, compared to that of other large faults in Asia such as Kunlun, Haiyuan, and Altyn Tagh (3-5). Previous attempts to determine the rate have produced disparate values ranging from 1 to 30 mm/year (2, 6-11). Such disparities may result from the different techniques applied and time periods observed, the part of the fault investigated, or its complex geometry, which displays multiple splays with oblique slip (12). We present measurements of the Mid- to Late Pleistocene slip rate on the southern stretch of the fault, based on 10Be surface exposure dating of two moraine crests displaced by the fault at the Manikala glacial valley terminus (32°2.529'N, 80°1.212'E, 4365 to 4760 m above sea level) (Figs. 1 and 2).

''Laboratoire de Tectonique, Mécanique de la Lithosphère, Unité Mixte de Recherche (UMR) 7578, CNRS, Institut de Physique du Globe de Paris, 75252 Paris Cedex 05, France. 2Insitute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. 3Institut de Physique du Globe de Strasbourg, UMR 7516, CNRS, Strasbourg, France. 4Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China. 5Total Exploration China, TotalFina-Elf, Beijing, 100004, China.

*To whom correspondence should be addressed. E-mail: [email protected]

The Manikala moraine complex lies at the base of the faulted Ayilari range front, which bounds the west side of the Gar valley, a large pull-apart basin floored by marshland that hides other strands of the Karakorum Fault system (13) (Fig. 1). The moraines, M1 and M2, lie southeast of the U-shaped Manikala Valley, a glacial trough deeply entrenched into the range's igneous basement (Fig. 2 and fig. S1). The range front is marked by triangular facets as high as 800 m that testify to a normal component of slip on the fault. The principal strand of the fault shows discrete right-lateral offsets (10 ± 2 m, 35 ± 5 m, and 75 ± 5 m) of young rills of different depths, incised into postglacial colluvium (fig. S1). Within the till complex, two main groups of moraines are recognized (Fig. 2 and fig. S2). All were emplaced by the Manikala Daer glacier, whose terminus is today ~7 km upstream. The morphology of the moraines indicates that they correspond to major advances of the glacier and were later abandoned when the glacier retreated upstream (fig. S3).

The relative ages of the moraine groups can be qualitatively assessed from their surface characteristics (Fig. 2 and fig. S2). The M1 surface is rough and composed of chaotically distributed, imbricate blocks (as large as 3 m in diameter) surrounded by coarse debris. The smoother surface of M2 appears older, with blocks (tens of centimeters to a meter in diameter) protruding above a mantle of smaller debris (Fig. 2 and fig. S2). The morainic ridges thus appear to become younger from east to west, consistent with right-lateral motion on the fault.

The M2 moraine complex is divided into eastern and western sections (M2E and

The peaks in the overall M1-M2 age distribution correspond to the coldest periods (~19, 36, 151, and 182 ka) as derived from proxy paleotemperature records, such as the SPECMAP 518O curve (16) (Fig. 3B), and hence to maximal glacial advances. In particular, 140 ± 5.5 ky (the younger M2 age group) corresponds roughly to the glacial maximum at the end of Marine Isotope Stage (MIS) 6 [150 to 140 ky ago (ka)], 40 ± 3 ky (the older M1 subgroup) to the cold period at the end of MIS 3 (-40 ka), and 21 ± 1.0 ky

Fig. 1. (A) Map of the major active faults of western Tibet; extensional/normal faults are denoted by tick marks, and compressional/thrust faults by teeth along their lengths. Red arrows show a subset of representative GPS velocities relative to Siberia (9, 72). Open ovals indicate the region of 1o error on velocity. The shaded rectangle shows the position of the InSAR swath used by Wright et al. (2). The open box indicates the position of Fig. 1B. (B) Map of the southern section of Karakorum Fault. The background map is a Shuttle Radar Topography Mission digital elevation model. Active branches of the Karakorum fault zone are outlined in red; other faults are in black. The open square is the Manikala moraine site; B and L are sites investigated by Brown et al. (6) and Lacassin et al. (7), respectively.

(WG-14 and WG-16 on M1) to the Last Glacial Maximum (LGM) (19 ka). The —20-and —40-ka advances are documented in the western Himalayas and Pakistan (17,18). The correlation implies that the mean ages obtained for the M1 and M2 moraines are not affected by erosion or snow cover. Cosmic-ray exposure before deposition and surface processes, coupled with the right-lateral fault motion of the till surfaces north of the fault (M2W, in particular) relative to the glaciers to the south, may contribute to the dispersion of the ages on M2. The oldest 10Be ages on M2E suggest that it was emplaced during the major glacial advance at the beginning of MIS 6, whereas the youngest ages on M2E are consistent with abandonment —140 ka, at the beginning of the Eemian interglacial (Fig. 3). The bulk of the ages on the younger M1 moraine are consistent with emplacement at —40 ka. However, the younger ages on this surface suggest that it was not abandoned until the onset of post-LGM warming after —20 ka.

Matching the 1520 ± 50 m offset of the M2E lateral moraine with the sample ages that approximate the end of the MIS 6 glacial maximum (140 ± 5.5 ka) yields an average slip rate of 10.9 ± 0.6 mm/year. Likewise, matching the 220 ± 10 m offset of M1 with the age of the M1 LGM samples (21 ± 1.0 ky) yields a rate of 10.5 ± 0.5 mm/year. In contrast, if we associate the measured offsets with the older ages for samples on the M2E and M1 moraines (181 ± 14 and 40 ± 3 ky, respectively), we obtain disparate rates of 8.4 ± 0.8 and 5.5 ± 0.5 mm/year, respectively (fig. S5). Reconciling these rates would imply a rate of —9.2 mm/year between 181 and 40 ka and a factor of two recent velocity decreases without any plausible, independent tectonic justification. We conclude, therefore, that a Mid- to Late Pleistocene right-lateral slip rate of 10.7 ± 0.7 mm/year on this segment of the Karakorum Fault is most probable. The total rate of displacement between southwest-

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