Fisher’s Quantum Cognition
Condensed matter physicist Matthew Fisher proposes that quantum processing with nuclear spins might be operative in the brain and key to its functioning. He identifies “phosphorus as the unique biological element with a nuclear spin that can serve as a qubit for such putative quantum processing—a neural qubit—while the phosphate ion is the only possible qubit-transporter.”
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Matthew Fisher
Professor of Physics
Matthew P. A. Fisher is an American theoretical physicist and professor at UC Santa Barbara, renowned for his contributions to condensed matter physics. He has received the Alan T. Waterman Award and the Oliver E. Buckley Prize, and is a member of the National Academy of Sciences.
Key Takeaways
Core Claim
Consciousness may involve quantum computation in the brain using phosphorus nuclear spins as neural qubits.
How It Works
Phosphorus atoms in “Posner molecules” preserve entanglement, influencing neuron firing via calcium release.
Distinguishing Idea
Identifies a concrete biological structure (Posner molecule) as a long-lived quantum memory in the brain.
Implications
Points to a possible bridge between quantum biology and neuroscience, sparking a new “quantum neuroscience” field.
Open Issue
Experimental proof of Posner molecule quantum effects in living brains is still lacking.
Fisher’s Quantum Cognition
Condensed matter physicist Matthew Fisher proposes that quantum processing with nuclear spins might be operative in the brain and key to its functioning. He identifies “phosphorus as the unique biological element with a nuclear spin that can serve as a qubit for such putative quantum processing—a neural qubit—while the phosphate ion is the only possible qubit-transporter.” He suggests the “Posner molecule” (calcium phosphate clusters, Ca9(PO4)6) as “the unique molecule that can protect the neural qubits on very long times and thereby serve as a (working) quantum-memory” (Fisher, 2015).
Neural Qubits and Posner Molecules
To be functionally relevant in the brain, he says, “the dynamics and quantum entanglement of the phosphorus nuclear spins must be capable of modulating the excitability and signaling of neurons”—which he takes as a working definition of “quantum cognition”. Phosphate uptake by neurons, he says, might provide the critical link.
Quantum Entanglement and Neuroscience
Because quantum processing requires quantum entanglement, Fisher argues that “the enzyme catalyzed chemical reaction which breaks a pyrophosphate ion into two phosphate ions can quantum entangle pairs of qubits,” and that “Posner molecules, formed by binding such phosphate pairs with extracellular calcium ions, will inherit the nuclear spin entanglement.” Continuing the explanatory sequence, Fisher says “Quantum measurements can occur when a pair of Posner molecules chemically bind and subsequently melt, releasing a shower of intra-cellular calcium ions that can trigger further neurotransmitter release and enhance the probability of post-synaptic neuron firing. Multiple entangled Posner molecules, triggering non-local quantum correlations of neuron firing rates, would provide the key mechanism for neural quantum processing” (Fisher, 2015).
The possible centrality of quantum processing in the brain is supported by the emerging field of quantum biology. It can be called, “quantum neuroscience” (Ouellette, 2016). Fisher's proposal, even if incorrect in its specifics, is useful in identifying the kinds of processes and sequences of explanatory steps required if quantum processing is to be fundamental for brain function in general and for consciousness in particular.
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