Noise: It Turns Out You Need It

We don’t know whether quantum physics proves the universe is truly a strange place or that we are living in a virtual reality simulation, but we know it turns a lot of common sense into garbage. Take noise, for example. Noise — as in random electrical noise — is bad, right? We spend a lot of time designing to minimize noise. Researchers in Austria, Germany, and Australia recently published a paper that shows that noise can actually improve the flow of energy. While the paper is behind a paywall, the Focus article is available and, of course, you can probably find a copy of the paper if you want to read the entire thing.

The paper, titled “Environment-Assisted Quantum Transport in a 10-qubit Network” uses trapped calcium atoms to study an effect suspected of being a key factor in high-efficiency energy transfer such as the transfer observed in optical fibers and photosynthesis.

In a perfect material, you can imagine energy transfer — such as current flow through a conductor — as a wave of energy moving through the material. In the case of electric current, that wave is built from electrons, but it could also, for example, be photons. In either case, in general, the waves stay coherent through the material. But imperfections and defects can destroy coherency and cause wave interference where the trough of one wave cancels the peak of another one nearby. This effect is called Anderson (or strong) localization. However, this loss is at a maximum when the waves are totally out of phase with each other. Noise in the system makes it more likely that the waves will change phase relationship and reduce Anderson localization which boosts transfer efficiency.

The ten atoms formed a chain where researchers could use a laser to inject energy into the system and then watch it flow to the end of the chain. Other lasers can introduce disorder into the array, causing the Anderson localization effect. With a stable setup, Anderson localization caused inefficiency in energy transport. However, introducing noise into the disordered system reduced the effect of the Anderson localization — to a point. At some higher level, the noise caused an increased loss due to the Zeno effect.

It turns out that impurities and noise aren’t always bad things. We are always amazed that we live in a time where we are learning about the universe at such a fine level of detail.

15 thoughts on “Noise: It Turns Out You Need It

  1. ” Researchers in Austria, Germany, and Australia recently published a paper that shows that noise can actually improve the flow of energy. While the paper is behind a paywall, the Focus article is available and, of course, you can probably find a copy of the paper if you want to read the entire thing.”

    I seem to remember something similar applied to nerve cells. Sometime the “work with” rather than the “push around” is the better way.

    1. When you say “their research” it makes it look like you are saying the researchers are the people putting their work behind a paywall.
      Far too often it isn’t under their control, that choice is made by the facility or university they are working for, and/or the publisher. Those are the people that deserve the blame.

  2. > , in general the waves say coherent through the material

    … should probably be “the waves stay” (instead of “say”)

    That said – this is just another proof of the old trick to use random(!) noise in order to reduce “clean” destruction. Even the oldest ADC and DAC used noise to increase the resolution on their highest order bits (to reduce the quantization effect of regular sample rates). You find the same approach everywhere where regularities (and coherence is a regularity) kills information. The disadvantage of a small “noise” (as in “dirt”) is usually more than evened out by the advantage of still getting information when the system would normally “fail” (destruct or obstruct information).

  3. Interesting.

    The first thing that came to my mind is a limitation of genetic algorithms.

    As the permutations (mutations) of a genetic algorithm increase there becomes an increasing dependency on the “quality” (or true randomness) of noise introduced to the system.

    Will … in the end we seek towards to the universe as an ultimate source of noise.

    Will that be the event of singularity?

    OK, that didn’t end well. :-p

  4. Adding noise is beneficial (if not absolutely necessary) and very common in many applications. For example, carefully adding noise to the input of an Analog to Digital Converter (ADC) actually improves the ADC’s performance. Google ADC Added Noise, a bunch of resources will pop up.

    1. Actually, not just any noise but unbiased (Gaussian) noise with a standard deviation of about 1/2 LSB. The way it works is that if the real value is (hiding) somewhere between two values, without noise the ADC will always hit the lower value, but if there’s (good) noise present, then over time, the ADC sees BOTH values often enough so that the AVERAGE of those measurements (which is the tricky part) approaches the TRUE value.

      This can also be used to improve (average) spectral purity of DAC generated signals such that the effect is to spread out the spectral spurs to allow some equipment to pass FCC emissions testing. It’s also used for some critical digital system clocks for that reason and to reduce the average noise spurs that may affect sensitive equipment that may lock on to those spurs. For DAC and oscillator use, the added noise process is called dithering. Search for “spread spectrum oscillator”.

      GPS “gold codes” used to spread their signals within the same frequency range, works that way too, since those codes have “noise like” properties in that the codes do not correlate to each other (i.e. don’t interfere with each other) “on average”.

      And as Ostracus’ comment hinted above, the same basic concept applies to our senses of vision and hearing (and probably other nerve related functions) in that if our sense’s nerves have some background noise, then like the ADC above, those senses can fire when the sum of the noise and sensor input is above the nerve’s threshold (so something to that effect).

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