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102:
atoms. In this regime of fast spin-exchange, all atoms in an ensemble rapidly change hyperfine states, spending the same amounts of time in each hyperfine state and causing the spin ensemble to precess more slowly but remain coherent. This so-called SERF regime can be reached by operating with sufficiently high alkali metal density (at higher temperature) and in sufficiently low magnetic field.
110:
1594:
101:
state of the atoms. Atoms in different hyperfine states do not precess coherently and thereby limit the coherence lifetime of the atoms. However, decoherence due to spin-exchange collisions can be nearly eliminated if the spin-exchange collisions occur much faster than the precession frequency of the
124:
Alkali metal atoms in the spin-exchange relaxation-free (SERF) regime with hyperfine state indicated by color precessing in the presence of a magnetic field experience two spin-exchange collisions in rapid succession which preserves total angular momentum but changes the hyperfine state, causing the
66:
A SERF magnetometer achieves very high magnetic field sensitivity by monitoring a high density vapor of alkali metal atoms precessing in a near-zero magnetic field. The sensitivity of SERF magnetometers improves upon traditional atomic magnetometers by eliminating the dominant cause of atomic spin
1630:
spectral resonance line polarizes the atoms. An orthogonal probe beam detects the precession using optical rotation of linearly polarized light. In a typical SERF magnetometer, the spins merely tip by a very small angle because the precession frequency is slow compared to the relaxation rates.
1602:
Alkali metal vapor of sufficient density is obtained by simply heating solid alkali metal inside the vapor cell. A typical SERF atomic magnetometer can take advantage of low noise diode lasers to polarize and monitor spin precession. Circularly polarized pumping light tuned to the
1084:
as indicated by magnetic resonance linewidth for atoms as a function of magnetic field. These lines represent operation with potassium vapor at 160, 180 and 200 °C (higher temperature provides higher relaxation rates) using a 2 cm diameter cell with 3 atm He buffer gas, 60 Torr
1031:
is the average polarization of the atoms. The atoms suffering fast spin-exchange precess more slowly when they are not fully polarized because they spend a fraction of the time in different hyperfine states precessing at different frequencies (or in the opposite direction).
113:
Alkali metal atoms with hyperfine state indicated by color precessing in the presence of a magnetic field experience a spin-exchange collision which preserves total angular momentum but changes the hyperfine state, causing the atoms to precess in opposite directions and
555:
1006:
293:
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Atomic magnetometer principle of operation, depicting alkali atoms polarized by a circularly polarized pump beam, precessing in the presence of a magnetic field and being detected by optical rotation of a linearly polarized probe
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62:
atoms and a very low magnetic field. Under these conditions, the atoms exchange spin quickly compared to their magnetic precession frequency so that the average spin interacts with the field and is not destroyed by decoherence.
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681:
408:
86:
sensitivity and can theoretically become even more sensitive with larger volumes. They are vector magnetometers capable of measuring all three components of the magnetic field simultaneously.
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In an optimal configuration, a density of 10 cm potassium atoms in a 1 cm vapor cell with ~3 atm helium buffer gas can achieve 10 aT Hz (10 T Hz) sensitivity with relaxation rate
1712:
but the application to magnetic field measurement was not explored at that time. The name "SERF" was partially motivated by its relationship to SQUID detectors in a marine metaphor.
1082:
831:
393:
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quenching gas. The SERF regime is clearly apparent for sufficiently low magnetic fields where the spin-exchange collisions occur much faster than the spin precession.
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atoms to precess in opposite directions only slightly before a second spin-exchange collision returns the atoms to the original hyperfine state.
402:
In the limit of fast spin-exchange and small magnetic field, the spin-exchange relaxation rate vanishes for sufficiently small magnetic field:
586:
1831:
Kominis, I. K.; Kornack, T. W.; Allred, J. C.; Romalis, M. V. (April 10, 2003). "A subfemtotesla multichannel atomic magnetometer".
1341:
In the absence of spin-exchange relaxation, a variety of other relaxation mechanisms contribute to the decoherence of atomic spin:
1549:
rates for collisions among the alkali metal atoms and collisions between alkali atoms and any other gasses that may be present.
1708:
in the early 2000s. The underlying physics governing the suppression spin-exchange relaxation was developed decades earlier by
2079:
550:{\displaystyle R_{se}={\frac {\gamma _{e}^{2}B^{2}T_{se}}{2\pi }}{\frac {1}{2}}\left(1-{\frac {(2I+1)^{2}}{Q^{2}}}\right)}
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580:
is the "slowing-down" constant to account for sharing of angular momentum between the electron and nuclear spins:
43:
in the early 2000s. SERF magnetometers measure magnetic fields by using lasers to detect the interaction between
94:
79:
detectors of equivalent size. A small 1 cm volume glass cell containing potassium vapor has reported 1 fT/
68:
51:
1678:
1042:
72:
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magnetometers for use in a variety of applications. The SERF magnetometer has the following advantages:
1001:{\displaystyle Q(I=7/2)=8\left({\frac {4(1+7P^{2}+7P^{4}+P^{6})}{11+35P^{2}+17P^{4}+P^{6}}}\right)^{-1}}
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1978:
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1928:"Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields"
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for atoms with low polarization experiencing slow spin-exchange can be expressed as follows:
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288:{\displaystyle R_{se}={\frac {1}{2\pi T_{se}}}\left({\frac {2I(2I-1)}{3(2I+1)^{2}}}\right)}
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1472:{\displaystyle R_{tot}=R_{D}+R_{sd,self}+R_{sd,\mathrm {He} }+R_{sd,\mathrm {N_{2}} }}
820:{\displaystyle Q(I=5/2)=6\left(3-{\frac {48(1+P^{2})}{19+26P^{2}+3P^{4}}}\right)^{-1}}
58:, is avoided in these magnetometers. This is done by using a high (10 cm) density of
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2059:
120:
1889:"Effect of rapid spin exchange on the magnetic-resonance spectrum of alkali vapors"
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Applications utilizing high sensitivity of SERF magnetometers potentially include:
44:
36:
1990:
1809:
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preserve total angular momentum of a colliding pair of atoms but can scramble the
1245:{\displaystyle \delta B={\frac {1}{\gamma }}{\sqrt {\frac {2R_{tot}Q}{F_{z}N}}}}
55:
2013:
1966:
1951:
1927:
1785:
1729:
1967:"Tunable Atomic Magnetometer for Detection of Radio-Frequency Magnetic Fields"
109:
71:
among the alkali metal atoms. SERF magnetometers are among the most sensitive
1912:
1888:
1786:"High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation"
1730:"High-sensitivity atomic magnetometer unaffected by spin-exchange relaxation"
59:
1998:
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1817:
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All-optical measurement limits enables imaging and eliminates interference
1852:
17:
2037:
1965:
I. M. Savukov; S. J. Seltzer; M. V. Romalis & K. L. Sauer (2005).
2012:
H. Xia; A. Ben-Amar
Baranga; D. Hoffman & M. V. Romalis (2006).
1784:
Allred, J. C.; Lyman, R. N.; Kornack, T. W.; Romalis, M. V. (2002).
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1034:
676:{\displaystyle Q(I=3/2)=4\left(2-{\frac {4}{3+P^{2}}}\right)^{-1}}
119:
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76:
1509:
is the relaxation rate due to collisions with the cell walls and
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of atomic magnetometers are limited by the number of atoms
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Sample magnetization measurement, especially rock samples
54:, a mechanism which usually scrambles the orientation of
2060:
The Spin
Exchange Relaxation Free (SERF) Magnetometer
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2014:"Magnetoencephalography with an atomic magnetometer"
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Allred JC, Lyman RN, Kornack TW, Romalis MV (2002).
50:
The name for the technique comes from the fact that
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1306:is the average polarization of total atomic spin
2056:from the Romalis Group at Princeton University.
328:is the time between spin-exchange collisions,
8:
1926:Savukov, I. M. & Romalis, M. V. (2005).
75:and in some cases exceed the performance of
1647:Equal or better sensitivity per unit volume
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47:atoms in a vapor and the magnetic field.
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1720:
1700:The SERF magnetometer was developed by
368:is the magnetic resonance frequency,
7:
1887:Happer, W. & Tam, A. C. (1977).
1077:{\displaystyle R_{tot}=Q\Delta \nu }
2054:Photographs of a SERF magnetometer
1457:
1432:
1429:
1141:and their spin coherence lifetime
1068:
133:The spin-exchange relaxation rate
14:
16:For the unfree peasant Serf, see
1664:Sensor vapor cell must be heated
1661:Can only operate near zero field
1639:SERF magnetometers compete with
1679:magnetoencephalographic imaging
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1:
1991:10.1103/PhysRevLett.95.063004
1810:10.1103/PhysRevLett.89.130801
1754:10.1103/PhysRevLett.89.130801
25:spin exchange relaxation-free
1635:Advantages and disadvantages
388:{\displaystyle \gamma _{e}}
2096:
1952:10.1103/PhysRevA.71.023405
106:
15:
1657:Potential disadvantages:
1913:10.1103/PhysRevA.16.1877
1538:{\displaystyle R_{sd,X}}
1114:{\displaystyle \delta B}
95:Spin-exchange collisions
90:Spin-exchange relaxation
69:spin-exchange collisions
52:spin exchange relaxation
2018:Applied Physics Letters
1971:Physical Review Letters
1578:{\displaystyle R_{tot}}
1268:{\displaystyle \gamma }
1697:
1696:SERF components mockup
1650:Cryogen-free operation
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321:{\displaystyle T_{se}}
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156:{\displaystyle R_{se}}
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73:magnetic field sensors
67:decoherence caused by
2080:Measuring instruments
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1625:
1623:{\displaystyle D_{1}}
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1502:{\displaystyle R_{D}}
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1333:
1331:{\displaystyle F=I+S}
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1299:{\displaystyle F_{z}}
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1161:{\displaystyle T_{2}}
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348:is the nuclear spin,
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1706:Princeton University
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361:{\displaystyle \nu }
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41:Princeton University
2075:American inventions
2030:2006ApPhL..89u1104X
1983:2005PhRvL..95f3004S
1944:2005PhRvA..71b3405S
1905:1977PhRvA..16.1877H
1853:10.1038/nature01484
1845:2003Natur.422..596K
1802:2002PhRvL..89m0801A
1746:2002PhRvL..89m0801A
445:
1702:Michael V. Romalis
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1277:gyromagnetic ratio
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2038:10.1063/1.2392722
1932:Physical Review A
1893:Physical Review A
1839:(6932): 596–599.
1677:High-performance
1589:Typical operation
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1195:
1134:{\displaystyle N}
1024:{\displaystyle P}
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573:{\displaystyle Q}
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341:{\displaystyle I}
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2048:External links
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2024:(21): 211104.
2004:
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1796:(13): 130801.
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2027:
2023:
2019:
2015:
2008:
2005:
2000:
1996:
1992:
1988:
1984:
1980:
1977:(6): 063004.
1976:
1972:
1968:
1961:
1958:
1953:
1949:
1945:
1941:
1938:(2): 023405.
1937:
1933:
1929:
1922:
1919:
1914:
1910:
1906:
1902:
1898:
1894:
1890:
1883:
1881:
1879:
1875:
1870:
1866:
1862:
1858:
1854:
1850:
1846:
1842:
1838:
1834:
1827:
1824:
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1790:Phys Rev Lett
1787:
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1734:Phys Rev Lett
1731:
1724:
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1646:
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1632:
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1588:
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1570:
1567:
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1560:
1550:
1548:
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1517:
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1490:
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39:developed at
38:
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34:
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559:
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297:
132:
93:
65:
56:atomic spins
49:
45:alkali metal
37:magnetometer
33:magnetometer
32:
28:
24:
22:
1094:Sensitivity
2069:Categories
1716:References
1263:γ
1193:γ
1179:δ
1106:δ
1072:ν
1069:Δ
991:−
810:−
733:−
666:−
632:−
499:−
475:π
433:γ
377:γ
356:ν
240:−
199:π
114:decohere.
99:hyperfine
60:potassium
1999:16090946
1861:12686995
1818:12225013
1762:12225013
1545:are the
2026:Bibcode
1979:Bibcode
1940:Bibcode
1901:Bibcode
1869:4204465
1841:Bibcode
1798:Bibcode
1742:Bibcode
1688:History
1275:is the
395:is the
81:√
18:Serfdom
1997:
1867:
1859:
1833:Nature
1816:
1760:
1482:where
1255:where
1011:where
560:where
298:where
1865:S2CID
1641:SQUID
1598:beam.
77:SQUID
1995:PMID
1857:PMID
1814:PMID
1758:PMID
29:SERF
2034:doi
1987:doi
1948:doi
1909:doi
1849:doi
1837:422
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1750:doi
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27:(
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