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posted by Fnord666 on Sunday January 07 2018, @08:57PM   Printer-friendly
from the quantum-is-the-new-blockchain dept.

National Institute of Standards and Technology (NIST) researchers have used sensitive optically pumped magnetometers to detect low frequency magnetic signals while ignoring noise, effectively boosting their range:

The NIST team is experimenting with low-frequency magnetic radio—very low frequency (VLF) digitally modulated magnetic signals—which can travel farther through building materials, water and soil than conventional electromagnetic communications signals at higher frequencies.

VLF electromagnetic fields are already used underwater in submarine communications. But there's not enough data-carrying capacity for audio or video, just one-way texts. Submarines also must tow cumbersome antenna cables, slow down and rise to periscope depth (18 meters, or about 60 feet, below the surface) to communicate. "The big issues with very low-frequency communications, including magnetic radio, is poor receiver sensitivity and extremely limited bandwidth of existing transmitters and receivers. This means the data rate is zilch," NIST project leader Dave Howe said. "The best magnetic field sensitivity is obtained using quantum sensors. The increased sensitivity leads in principle to longer communications range. The quantum approach also offers the possibility to get high bandwidth communications like a cellphone has. We need bandwidth to communicate with audio underwater and in other forbidding environments," he said.

As a step toward that goal, the NIST researchers demonstrated detection of digitally modulated magnetic signals, that is, messages consisting of digital bits 0 and 1, by a magnetic-field sensor that relies on the quantum properties of rubidium atoms. The NIST technique varies magnetic fields to modulate or control the frequency—specifically, the horizontal and vertical positions of the signal's waveform—produced by the atoms. "Atoms offer very fast response plus very high sensitivity," Howe said. "Classical communications involves a tradeoff between bandwidth and sensitivity. We can now get both with quantum sensors."

Traditionally, such atomic magnetometers are used to measure naturally occurring magnetic fields, but in this NIST project, they are being used to receive coded communications signals. In the future, the NIST team plans to develop improved transmitters. The researchers have published their results [open, DOI: 10.1063/1.5003821] [DX] in the Review of Scientific Instruments.

From the paper:

For communications, the channel capacity is the best performance metric since it directly measures the bit rate for a given range. We use the link budget described in Sec. II E and shown in Fig. 4. With the ambient noise-determined sensor baseline of 100 pT/Hz and SNR = 2 at the sensor (corresponding to the last row of Table II), the channel capacity is about 2.3 bits/s, achieved at a range of 37 m at 1 Hz bandwidth. For chip rates (or bandwidth) of 30 Hz and 180 Hz, the channel capacity is correspondingly 70 bits/s and 418 bits/s. With a sensor baseline of 300 fT/Hz (budgeting for ambient noise cancellation using more than one OPM with a 100 fT/Hz baseline), as shown in Fig. 4, these channel capacities would be obtained at 320 m range.

[...] It is important to stress that the signals measured by OPMs can penetrate media that displays orders of magnitude more loss at higher frequencies at the cost of lower bandwidth or more integration time. Therefore, comparisons with higher capacity channels or spatial location uncertainties should consider the propagation through such media as water, rock, snow, and even metals.

Also at Newsweek.


Original Submission

 
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  • (Score: 2) by JoeMerchant on Monday January 08 2018, @02:06AM

    by JoeMerchant (3937) on Monday January 08 2018, @02:06AM (#619359)

    This isn't that kind of quantum....

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