Time-multiplexed dual atomic magnetometry
Time-multiplexed atomic magnetometry uses first and second atomic vapor cells to measure an external magnetic field. Each vapor cell operates according to a sequence of alternating pumping and probing stages. However, the sequences are temporally offset from each other such that the second vapor cell is pumped while the first vapor cell is probed, and the first vapor cell is pumped while the second vapor cell is probed. With this time-multiplexed operation, the external magnetic field can be measured without any time gaps. The Hilbert transform of the signals may be taken to obtain their instantaneous phases, which may then be interleaved to form a single gapless time sequence that represents the external magnetic field over a time window that lasts for several continuous pumping/probing stages.
1. A time-multiplexed dual atomic magnetometer, comprising:
first and second vapor cells positioned such that an external magnetic field induces Larmor precession of atoms within the first and second vapor cells;
a first polarimeter configured to:
measure a first polarization of a first probe beam after the first probe beam propagates through the first vapor cell; and
output a first polarization signal indicative of the first polarization;
a second polarimeter configured to:
measure a second polarization of a second probe beam after the second probe beam propagates through the second vapor cell; and
output a second polarization signal indicative of the second polarization; and
a signal processor configured to:
process the first polarization signal to obtain a first data block that represents the first polarization signal during a first measurement stage;
process the second polarization signal to obtain a second data block that represents the second polarization signal during a second measurement stage that starts when the first measurement stage ends; and
append the second data block to the first data block to obtain a temporal sequence that represents the external magnetic field during the first and second measurement stages.
2. The time-multiplexed dual atomic magnetometer of claim 1 , wherein the signal processor is configured to:
perform instantaneous-phase retrieval on the first data block to obtain a first magnetic-field sequence;
perform instantaneous-phase retrieval on the second data block to obtain a second magnetic-field sequence; and
append the second magnetic-field sequence to the first magnetic-field sequence to obtain the temporal sequence.
3. The time-multiplexed dual atomic magnetometer of claim 1 , wherein the signal processor is configured to output the temporal sequence.
4. The time-multiplexed dual atomic magnetometer of claim 1 , further comprising a controller configured to gate the first and second probe beams such that:
the first probe beam only propagates through the first vapor cell during the first measurement stage; and
the second probe beam only propagates through the second vapor cell during the second measurement stage.
5. The time-multiplexed dual atomic magnetometer of claim 4 , wherein the first and second measurement stages have the same duration.
6. The time-multiplexed dual atomic magnetometer of claim 4 , wherein the controller is configured to gate a first pump beam and a second pump beam such that:
the first pump beam only propagates through the first vapor cell during a first pumping stage prior to the first measurement stage, the first pump beam spin-polarizing the atoms in the first vapor cell; and
the second pump beam only propagates through the second vapor cell during a second pumping stage prior to the second measurement stage, the second pump beam spin-polarizing the atoms in the second vapor cell.
7. The time-multiplexed dual atomic magnetometer of claim 6 , wherein the first and second pumping stages have the same duration.
8. The time-multiplexed dual atomic magnetometer of claim 1 , further comprising at least one magnetic field coil that, when electrically driven, applies a magnetic bias field to the first and second vapor cells.
9. The time-multiplexed dual atomic magnetometer of claim 8 , wherein:
the first and second probe beams propagate along a common propagation direction; and
the at least one magnetic field coil is positioned such that the magnetic bias field is parallel to the common propagation direction.
10. The time-multiplexed dual atomic magnetometer of claim 8 , wherein:
the first and second probe beams propagate along a common propagation direction; and
the at least one magnetic field coil is positioned such that the magnetic bias field is perpendicular to the common propagation direction.
11. A method for time-multiplexed dual atomic magnetometry, comprising:
inducing, with an external magnetic field, Larmor precession of atoms that are located within first and second vapor cells;
measuring, with a first polarimeter, a first polarization of a first probe beam after the first probe beam propagates through the first vapor cell, the first polarimeter outputting a first polarization signal indicative of the first polarization;
measuring, with a second polarimeter, a second polarization of a second probe beam after the second probe beam propagates through the second vapor cell, the second polarimeter outputting a second polarization signal indicative of the second polarization; and
processing the first polarization signal to obtain a first data block that represents the first polarization signal during a first measurement stage;
processing the second polarization signal to obtain a second data block that represents the second polarization signal during a second measurement stage that starts when the first measurement stage ends; and
appending the second data block to the first data block to obtain a temporal sequence that represents the external magnetic field during the first and second measurement stages.
12. The method of claim 11 , wherein:
said processing the first polarization signal includes performing instantaneous-phase retrieval on the first data block to obtain a first magnetic-field sequence;
said processing the second polarization signal includes performing instantaneous-phase retrieval on the second data block to obtain a second magnetic-field sequence; and
said appending includes appending the second magnetic-field sequence to the first magnetic-field sequence.
13. The method of claim 11 , further comprising outputting the temporal sequence.
14. The method of claim 11 , further comprising gating the first and second probe beams such that:
the first probe beam only propagates through the first vapor cell during the first measurement stage; and
the second probe beam only propagates through the second vapor cell during the second measurement stage.
15. The method of claim 14 , wherein said gating the first and second probe beams includes gating the first and second probe beams such that the first and second measurement stages have the same duration.
16. The method of claim 14 , further comprising gating a first pump beam and a second pump beam such that:
the first pump beam only propagates through the first vapor cell during a first pumping stage prior to the first measurement stage, the first pump beam spin-polarizing the atoms in the first vapor cell; and
the second pump beam only propagates through the second vapor cell during a second pumping stage prior to the second measurement stage, the second pump beam spin-polarizing the atoms in the second vapor cell.
17. The method of claim 16 , wherein said gating the first and second pump beams includes gating the first and second pump beams such that the first and second pumping stages have the same duration.
18. The method of claim 11 , further comprising applying a magnetic bias field to the first and second vapor cells.
19. The method of claim 18 , wherein said applying includes applying the magnetic bias field such that a direction of the magnetic bias field is parallel to a common propagation direction of the first and second probe beams.
20. The method of claim 18 , wherein said applying includes applying the magnetic bias field such that a direction of the magnetic bias field is perpendicular to a common propagation direction of the first and second probe beams.