Is anyone doing continuous quantum measurements? Are you picking up gravity, seismic, magnetic, ELF and other noise?
As the quantum detectors get more sensitivity they should be picking up fluctuations in the local gravitational potential and electromagnetic background fields of the earth. But I have not seen anyone running a detector continuously for the days or weeks or months needed to do the required correlations to trace things out. Nor, do I see anyone using time of flight (array imaging with speed of light and speed of gravity) to correlate and image and characterize sources.
For many years I have been tracking every new gravimeter design – traditional sensitive accelerometers, atom interferometer gravimeters, MEMS gravimeters, electrochemical gravimeters, electron interferometer gravimeters, Bose Einstein gravimeters, and many others. If I left out your favorite gravimeter (also gradiometer and other names), tell me and I will add it to my list.
The problem with most of them is they are too slow to sort out natural, man-made and purpose build signals. You need at least Msps (mega samples per second) which is 300 meters resolution for many global sources. But there are many ADCs (analog to digital converters) that can do Gsps (giga sps) for relatively easy correlations.
The seismometer networks pick up a small bit of gravitational noise, as do the magnetometer networks, as do many electromagnetic sensor networks. It is taking a long time for all the groups to sort out, mostly “not my job”. But if there were some decent, low cost sensors that were sensitivity enough to track acceleration in real time (Gsps is real time for these sorts of things) maybe we could separate and characterize the sources.
I am writing to everyone, so some groups are very sophisticated but don’t do practical things. And other groups have practical problems, but no time or resources for theory. And all the groups are struggling with sharing data and models, ideas and problems globally.
Anyway, I know there are lots of “quantum” and “condensate” and other devices out there that have noise. I am asking all the groups to share their noise and sort it out. Much of the “kT” noise is partly magnetic, partly gravitational and much human activity. It is possible to separate. But it means serious effort for global correlations. Now the radio telescope groups have “correlators” and seismic groups have their methods, and electromagnetic groups their methods, and gravitational groups their methods. But it is just one field.
Regardless. If you have noise that propagates at the speed of light and gravity, then all the other groups are picking up part, or all your signals too. If you are tracking signals propagating at acoustic speeds and particle speeds then you should also be checking the speed of light and gravity signals – because there are almost always couplings – that show up in correlations.
And, if you are one of those rare people who also check for instantaneous signals (or ones that are billions of times the speed of light scale) then there are screens and checks for those too.
But here I am particularly asking for those “quantum” groups who find analog signals in their devices when they try to reduce the size, increase the frequency, lower the temperature — and all the thing people are doing to get to “nano”, “pico”, “femto”, “atto”, “zepto”. “yocto” scale phenomena.
Please update your notes on noise. Those strong millivolt, microvolt and nanovolt signals are just the start of many levels of tracking noise sources. If you have distributed sources it looks more like diffusion than shock waves or pulses. The signal from an earthquake is going to propagate at the speed of light and gravity, but it is going to have cubic kilometers of source. It is trackable, but it needs low cost detectors of high sensitivity and high sampling rates – then the arrays can image and track the seismic waves. That is just one of many hundreds of outstanding problems that need better detectors. I am hoping some of the groups who have been pushing hard to make “quantum device” will take a few moments to look at their noise seriously and think of the practical applications and problems of using those for imaging.
The signal at a superconducting gravimeter is about 95% sun moon tidal signal. That is about +/- 1000 nanometers per second squared (nm/s2) at one sample per second (sps). And the remaining 5% is from the atmosphere and nearby water and a tiny bit of magma. There will be the usual magnetic noise and electromagnetic noise from nanoHertz to GigaHertz. But some of it is gravitational – at least it shows up as a signal in a gravimeter or gradiometer or direct gravitational potential sensor (time dilation, Mossbauer, LIGO type detectors).
A “good” gravimeter array can image the local atmospheric density, flows, radiation field. That is a strong signal. You can convert gravitational signals to magnetic units by using B = 38.7083 g, where B is in Tesla and g is in meters/second^2. The earth field, 9.8 m/s2 comes to about 379 Tesla. That is why gravity is so fine grained and powerful. And why it is so hard to make strong magnets in the fluctuating earths gravitational field.
The tidal gravitational field is fairly smooth, but it can also be turbulent. You are just as likely to see “flow noise” than “sparks” or “shocks” or “pulses”. And lots of slow drifts and sudden changes of levels. It is not hard, but requires care and effort.
I have been at this for several decades. I take this unusual step of asking “anyone with noise” to contact me. If you have shielded your device from electric field variations, and done some magnetic shielding and still getting drift and variations, then it is “gravitational”.
I can tell you the rough size at the surface of the earth. A lot of the “kT” noise is gravitational flow noise. It is actually moving at the speed of light and gravity but you only see the net as a slow motion. The potential is smooth and has tiny gradients. You can see the gradients fairly easily. The “grain” is about one 7 millionth the mass of the electron and the size is picometers. The ultimate grain is not as small as the Planck scale, but on the order of 10^-24 meters. For practical things it is only necessary to work at 10^-18 scale. But use them all and you don’t have to stop at boundaries.
Electrons have mass, charge and magnetic moment – so they pick up electric, electromagnetic, acoustic and gravitational noise (signals if you know where it comes from). Just as electron paramagnetic resonance has advantages of higher speeds and greater sensitivity, so too does any electron or hole based device have advantages for detection and characterization of fast and tiny signals. I spent several years checking – the camera electron (or hole) wells are sensitive enough to use for detecting gravitational variations – and there are plenty of tiny escape events to work with. The same for all the memory devices – they are just small floating islands of a few electrons each. Sorting out the noise in the memory chips will help shrink those down to single electron charge levels and below.
It is possible to image the atmosphere with gravitational arrays. Since I am lumping magnetic and gravitational fields together now, that means any combinations of “gravimeters” or “magnetometers” or “electromagnetic (from nanoHertz to PetaHertz or more). Moving sensors get a synthetic aperture advantage. So if someone would boost the GRACE type satellites to monitor the motion of electrons at Gsps rates we could get clear, real time images of the earths interior. Likewise moving sensor detectors arrays for volcanoes, ocean currents, density variations, magma and other things. The “moving” can be from seismic or natural vibrations, just measure it carefully for correlations and corrections. It jinks the position of the sensor so you can use subpixel methods. Deliberate movements are fine, but random but measured ones work too.
Richard Collins, Director, The Internet Foundation
