How similar is the quantum computer to the human brain?

By Vedangana Saini, Ph.D, in Neuroscience

The human brain has phenomenal perception, memory processing, and critical thinking capabilities. Those capabilities make it the most powerful computing device known to mankind. In a way, the classical computer and the human brain have a somewhat similar mode of operation. Both of them receive and process information and make decisions. However, there are several complex tasks performed by the human brain that cannot be simply explained by it working as a classical computer with the designated input and output channels. For example, the ability of the human brain to process memories at an extremely rapid rate using relatively slow cells or neurons cannot be explained by comparing it to a traditional computer. To explain the capabilities of the human brain, scientists have theorised that the it uses quantum mechanics for high-speed memory processing and that complex processes like consciousness can be better understood by considering that the human brain and quantum computers use similar mechanisms, but how accurate is this analogy?

What are quantum computers and how do they work?

Classical computers are binary, i.e. they use two states or bits like 0s and 1s to perform all the calculations and operations. A quantum computer, on the other hand uses quantum states of an object to carry out all the calculations. This means that a for quantum computer an object does not have a fixed value like 0s and 1s, but instead, the object can be at any state or a vibration phase such as the spin of an electron. The basic unit of operation of a quantum computer is qubit. A qubit can be both 0 and 1 at the same time. It can be a superposition of multiple states and values. Since the quantum computer performs operations based on the probability of the state of an object at any given time, it can analyze multiple possibilities and do several iterations. Thus,  the main implication of quantum computing is that they have a potential to process quickly analyze a large number of data and create a complex processing network somewhat similar to the human brain.

The human brain vs. the quantum computer

Several scientists have suggested that the human brain is not entirely a biochemical system, but rather, it behaves as a macroscopic quantum system. The human brain is the commanding center that perceives, analyzes and meets the body’s specific genetic and physiological demands by precisely coordinating the network of cells within it. This coordination among the neurons and the networks of neurons is based on the interaction between several molecules, atoms, and subatomic particles. As a result, the cells of the human brain and body remain connected and talk with each other even form a distance i.e. they remain entangled. This entanglement is a quantum feature.

Entanglement from the perspective of quantum physics

From the perspective of quantum physics, entanglement allows qubits to remain intertwined and stay in different states at once and quickly process information and change their state as required. An Oxford mathematician named Roger Penrose hypothesized that the protein tubes, called microtubules in the brain cells interact with each other and make this entanglement possible. Due to this interaction, the human brain can analyze a problem and devise several answers simultaneously and iterate those answers in different combinations like a quantum computer does. According to Penrose, the quantum physics of the tiny microtubules in the human brain explain human genius and the complex phenomenon known as the human consciousness.

In other words, we can say that the brain cells are aware of each other’s biochemical and electric state and they work in superb coherence or coordination. Such coherence is, in fact, orginially seen in processing of odours by the brain cells. Several studies are emerging to explain human learning, memory, perception and various mental states by using the laws of quantum mechanics. It is still not clear, however, how drugs and pharmaceuticals alter one’s state of mind. There are theories now that suggest that the drugs may not be acting on a single receptor in the brain cells. By taking into account the quantum mechanics principles, it can be assumed that drugs may be triggering a larger change by influencing several kinds of cells and pathways in the brain. Thus, generating millions of possibilities in which a person’s mind may act or interact with them. Similarly, quantum physics may explain why different people have different clinical presentation of Alzheimer’s or Parkinson’s diseases and the way individuals uniquely interact with anaesthesia (14). 

Is there a catch in these theories?

There are scientists who do not fully agree with the theory that the human brain and quantum computers work in the exact same way. For example, scientists from the University of Waterloo, Ontario, argue that complex mental functions such as consciousness, can also be explained by neurocomputation. According to proponents of neurocomputation, the neurons act as a single, huge, and massively repeated “circuit” which follows the standard logic gate, input-output systems like a classical computer and there is no quantum physics involved. Recent developments in artificial intelligence such as the use of deep learning networks in language and speech recognition indicate the ability of the classical computer to behave like a human brain.

Furthermore, scientists also argue that in order for qubits to maintain their coherent state and superposition, they must work at a very low temperature and be well isolated from interference. Attaining this much lower temperature and isolation is not possible in the human brain. However, this is not entirely the case. Some theories claim that once the qubits reach a particular intertwined state, they can maintain coherence even at the ordinary temperature. So, there is no clear evidence that quantum mechanics do not play a role in the functioning of the human brain.


Both classical and quantum computers process information, albeit at remarkably different speeds. The human brain does more than that. In addition to cognition, it coordinates the work of all physiological systems in the body, enabling the organism to survive. And while both types of computers (the classical and the quantum) can learn from the human brain, we do not fully understand how the brain works yet.

In the field of neuroscience, a lot remains unexplained, mysterious and puzzling. To get more insights into the implications of quantum mechanics in the operation of human brain, scientists need to explore and understand the quantum events occurring inside a single brain cell and scale it up to the organism level. There is still a long road ahead.


  1. De Barros, J. A., & Suppes, P. (2009). Quantum mechanics, interference, and the brain. Journal of Mathematical Psychology53(5), 306-313.
  2. Weiss, V. (1986). From memory span and mental speed toward the quantum mechanics of intelligence. Personality and Individual Differences7(5), 737-749.
  3. Hameroff, S., & Penrose, R. (1996). Orchestrated reduction of quantum coherence in brain microtubules: A model for consciousness. Mathematics and computers in simulation40(3-4), 453-480.
  4. Deutsch, D., & Jozsa, R. (1992). Rapid solution of problems by quantum computation. Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences439(1907), 553-558.
  5. Rakovic, D., Dugic, M., & Cirkovic, M. M. (2004). Macroscopic quantum effects in biophysics and consciousness. NeuroQuantology2(4).
  6. Hu, H., & Wu, M. (2005). Thinking outside the box: the essence and implications of quantum entanglement.
  7. Gardiner, J., Overall, R., & Marc, J. (2010). The Fractal Nature of the Brain: EEG Data Suggests That the Brain Functions as a” Quantum Computer” in 5-8 Dimensions. NeuroQuantology8(2).
  8. Conte, E., Khrennikov, A. Y., Todarello, O., Federici, A., Mendolicchio, L., & Zbilut, J. P. (2009). Mental states follow quantum mechanics during perception and cognition of ambiguous figures. Open Systems & Information Dynamics16(01), 85-100.
  9. Atmanspacher, H. (2004). Quantum theory and consciousness: An overview with selected examples. Discrete dynamics in Nature and Society2004(1), 51-73.
  10. Aerts, D., & Aerts, S. (1995). Applications of quantum statistics in psychological studies of decision processes. Foundations of Science1(1), 85-97.
  11. Green, J. P., & Weinstein, H. (1981). Recognition, response: quantum mechanics can account for the affinities of drugs and receptors. The Sciences21(7), 27-29.
  12. Kuljiš, R. O. (2010). Integrative understanding of emergent brain properties, quantum brain hypotheses, and connectome alterations in dementia are key challenges to conquer Alzheimer’s disease. Frontiers in neurology1, 15.
  13. Tarlaci, S. (2010). A historical view of the relation between quantum mechanics and the brain: a neuroquantologic perspective. NeuroQuantology8(2).
  14. Hameroff, S. (1998). Anesthesia, consciousness and hydrophobic pockets—A unitary quantum hypothesis of anesthetic action. Toxicology letters100, 31-39.
  15. Hameroff, S. R. (2007). The brain is both neurocomputer and quantum computer. Cognitive Science31(6), 1035-1045.
  16. Marcus, G., Marblestone, A., & Dean, T. (2014). The atoms of neural computation. Science346(6209), 551-552.
  17. Litt, A., Eliasmith, C., Kroon, F. W., Weinstein, S., & Thagard, P. (2006). Is the brain a quantum computer?. Cognitive Science30(3), 593-603.
  18. Hameroff, S., & Penrose, R. (2014). Reply to criticism of the ‘Orch OR qubit’–‘Orchestrated objective reduction’is scientifically justified. Physics of Life Reviews11(1), 94-100.