The following is an extract from our Lost in Space-Time newsletter. Each month, we hand over the keyboard to a physicist or two to tell you about fascinating ideas from their corner of the universe. You can sign up for Lost in Space-Time for free here.
For years I underestimated nature. As a quantum physicist, my interests simply didn’t extend to the biological. I was fascinated by particles and forces, not cells and organisms. Then one day that all changed, when I realised nature is a better quantum engineer than me.
I was one year into a postdoctoral project that involved putting biochemicals on top of a nano-sized thing. The details don’t really matter, but what’s important is that the biochemicals were not doing what they were meant to be doing, and I found myself looking for alternatives. I started haphazardly reading about a protein that senses magnetic fields in a way I thought was only possible with high-tech quantum experiments. But there was no doubt: This was bona fide “quantum sensing”.
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I had already spent years building instruments to study and control the quantum properties of small things like electrons for the purpose of using them as electronic and magnetic field sensors. These quantum probes outperformed much larger sensors: Their quantumness actually improved the measurement.
Yet, here I was seeing that nature was already way ahead of the world of physics as constructed by humans: “Nature’s own quantum sensor, est. 1 billion years BC!!!”. How could this be? The idea that proteins behave in a quantum way seemed to go against my understanding of when quantumness breaks down and biology takes over.
żěè¶ĚĘÓƵs have known for more than a century that the rules of classical mechanics, like Newton’s laws of motion, break down at atomic scales and a different set of laws, known as quantum physics, takes control. To the naked eye, quantum physics can seem counterintuitive and somewhat magical. For example, in the quantum world, small objects such as electrons and atomic nuclei can be in two different places at once and “tunnel” through tiny energy barriers, appearing on the other side unscathed.
But as systems become larger – at, say, the scale of a whole protein or a solution containing millions of proteins – this quantumness disappears very fast. The macroscopic is better described by the laws of classical mechanics. Those tiny particles that are each concomitantly in two different places will, after a short while, settle on just one place – as expected classically.
In biology, researchers historically took for granted that quantum effects must disappear, washed out in what Erwin Schrödinger called the “warm, wet environment of the cell”. Most scientists still believe biology can be adequately described by classical physics: No funky barrier crossings, no being in multiple locations simultaneously.
However, there is increasing evidence that biology uses quantum properties to function and optimally respond to external stimuli, as is the case with the protein that senses magnetic fields.
Quantum sensing
The protein in question, like many, many others, senses magnetic fields because of something called a spin-dependent chemical reaction, involving both my favourite quantum object – the electron – and my favourite quantum property – spin.
Electrons possess spin, which is a fundamental property of matter, like mass and charge. While mass determines matter’s interaction with gravity and charge determines its interaction with electric fields, spin governs its interaction with magnetic fields. Different spin states, normally represented as up and down arrows, interact differently with magnetic fields.
Spin is distinctly quantum in nature, with particular magnetic fields being able to put a particle’s spin in a quantum state that encompasses both up and down simultaneously. This phenomenon is known as superposition.
Some chemical reactions are influenced by the superposition states of specific electron spins. Since magnetic fields can affect these states, they can also impact the macroscopic outcomes of these reactions. And this is exactly how the protein works: It interacts with, or “senses”, very tiny magnetic fields using electron spin as a quantum detector. And it can do this all at room temperature, in a messy solution with millions of molecules; in other words, within an environment where quantumness is not expected to survive for long, let alone to be used as a resource.
The exciting scientific frontier that I am currently working on involves the tantalising possibility that proteins inside living cells use quantum effects. Cellular environments are messy, and so the odds are against any quantumness, such as an electron spin superposition, surviving it to tell the tale.
Still, even though there is not yet a smoking gun proving that cells work this way, there is correlative evidence that electron spin-dependent chemical reactions do alter the function of living cells. Birds can sense Earth’s tiny magnetic field as a migratory cue. They seem to do so via a magnetosensitive protein called a cryptochrome – the very same protein that caught my attention all those years ago.
There is also evidence that weak magnetic fields lead to physiological responses across the tree of life, in vertebrates, invertebrates, plants and bacteria. These effects range from changes in DNA repair rates and the production of cellular oxidants to neurological function and cell metabolism, to name a few. So much of the machinery of how cells work appears to be tweakable by weak magnetic fields in a quantum manner.
All of this points to a coming revolution in our understanding of biology and the overlooked role that quantum physics plays in it. Researchers and companies are already looking for ways to harness weak magnetic fields, from medical efforts to reduce the size of tumours or boost muscle regeneration, to increasing the yield of lab-grown meat. However, there is still a long way to go before these efforts become a reality.
What is currently missing is a comprehensive understanding of exactly how different electron spin superposition states correspond to different physiological outcomes within a cell or tissue. But if we develop a quantum biology “codebook”, it could give us deterministic control over many of our physiological responses.
In my lab, we are working on this codebook. We hope that it will eventually lead to simple electronic devices that could produce electromagnetic interventions for disease prevention and more.
Humankind is only at the start of its journey to understand quantum mechanics. Over billions of years, nature has already become the ultimate quantum engineer.
leads the Quantum Biology Tech (QuBiT) Lab at the University of California, Los Angeles
