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Is the Human Brain a Quantum Computer?
Quantum computers employ quantum processors that use elementary particles like neutrons, electrons and/or atoms instead of integrated circuits and transistors like classical processors. Two of the most “crazy and magical” properties that these particles have include the following:
• Firstly, they are somehow continuously “connected” to other particles that are entangled with it after some interaction. For example, when one particle’s spin is measured in the “up” state, the other particle, even if it was very far away, would instantly (i.e. faster than the speed of light) be in the opposite “down” state. Large collections of entangled particles (if they existed in the brain) could therefore behave in an “orchestrated” or coordinated manner over long distances.
• Secondly, they exist in a superposition of states prior to any measurement. For example, an electron may be in two different energy levels or be spinning up and down at the same time. When measured, however, they will be at a specific energy level or spin direction – we say that they have “collapsed” to a particular state. When using classical processors, we assign a definite “1” or “0” to a bit. In a quantum processor, we could assign “1” to the spin-down state and “0” to the spin-up state of, say, an electron. However, until we measure the state, it will be “1” and “0” at the same time – just as a spinning coin is neither “heads” nor “tails” when it is spinning. Hence, one quantum bit or “qubit” can represent “1” AND “0” at the same time, unlike the classical processor’s “bit” which can only represent “1” OR “0” at a point in time. The bit is binary and point-like but the qubit is “space-like” and “fuzzy”; this allows much more information to be processed in parallel, taking advantage of the property of superpositions. A “bit” represents either a 1 or 0 at a point in time, whereas a “qubit” can represent both at once.1
Various physical attributes of elementary particles can be assigned the “1s” and “0s”. For example, we can use the spin-up or spin-down states of the nucleus of an atom, the different energy levels of electrons in an atom, or even the orientation of the plane of polarization of light particles or photons.
Quantum Computing using Phosphorus Atoms
In 2013, a research team led by Australian engineers from the University of New South Wales (UNSW) created the first working quantum bit based on the spin of the nucleus of a single phosphorus atom within a protective bed of non-magnetic silicon atoms with zero spin. In a ground-breaking paper in the journal Nature, they reported a record-high accuracy in writing and reading quantum information using the nuclear spin. 2
As the nucleus of a phosphorus atom has a very weak magnetic field and possesses the lowest spin number of ½ (which means it is less sensitive to electric and magnetic fields), it is nearly immune to magnetic noise or electrical interference from the environment. It is further “shielded” from noise by the surrounding bed of zero-spin silicon atoms. Consequently, the nuclear spin has a longer coherence time enabling information to be stored in it for a longer time, which results in a much higher level of accuracy.
“The core of the phosphorus atom contains a nuclear spin, which could act as an excellent memory storage qubit thanks to its very weak sensitivity to the noise present in the surrounding environment.”
Andrew Zurak, reporting on the UNSW Team’s Work, 3
In 2014, another team (this time a Dutch-US collaboration) used the nuclear spins of phosphorus atoms in quantum computing to achieve even greater accuracy of 99.99% and a longer coherence time of above 35 seconds. 4,5
Quantum Computers in our Heads?
So, what does all of this have to do with our brains? There are numerous examples in quantum biology where quantum processing has been suspected; for example, there is evidence that birds utilize quantum processes in their retinas to navigate across the globe and that photosynthesis proceeds more efficiently by achieving long-lived coherent quantum states. It has also been observed that the human sense of smell and certain aspects of human vision would require quantum processing to occur. So, it is no surprise that we should be looking for quantum processing in the human brain.
One of the first popular hypotheses was proposed by Roger Penrose, the distinguished physicist, and Stuart Hammeroff, an anesthesiologist. They speculated that quantum processing could be occurring in the microtubules of neurons.6 However, most scientists were skeptical as the brain was considered a warm, wet, and noisy environment where quantum coherence, which usually occurs in extremely isolated environments and cold temperatures, would be impossible to achieve. Neither Penrose nor Hammeroff have given a satisfactory response to this criticism of their theory. However, there have been recent breakthroughs in extending coherence times and research teams around the world are rushing to extend coherence times at room temperatures with some success.7,8 So, the jury is still out on the Penrose-Hammeroff theory.
Fisher’s Ground-breaking Ideas
More recently in 2015, Matthew Fisher, a physicist at the University of California, produced a model where nuclear spins in phosphorus atoms can serve as qubits. This model is much like what was discussed in the previous section in that it was developed in a laboratory setting; the exception is that this time it applied to the human brain, where phosphorus is abundant.9
“Might we, ourselves, be quantum computers, rather than just clever robots who are designing and building quantum computers?”
Matthew Fisher, 10
Fisher has argued quite convincingly that spins of the nuclei of phosphorus atoms can be sufficiently isolated (by the protective cloud of electrons around it and the protective shield of a bed of zero spin atoms) and also be less “distracted” by quantum noise because of its weak magnetic field (due to its low spin number), thus allowing it to preserve quantum coherence. (The laboratory studies discussed in the previous section and the experimental results have verified and confirmed this fact.) So, in an environment such as the brain where electric fields abound, the nuclei of phosphorus atoms would be in a sufficiently isolated environment.
The process starts in the cell with a chemical compound called pyrophosphate. It is made of two phosphates bonded together – each composed of a phosphorus atom surrounded by multiple oxygen atoms with zero spin (a similar situation as that of the laboratory study discussed above, where the phosphorus atom was nestled inside silicon atoms with zero spin). The interaction between the spins of the phosphates causes them to become entangled. One of the resulting configurations results in a zero spin, or a “singlet” state of maximum entanglement. Enzymes then break apart the entangled phosphates into two free phosphate ions, which continue to be entangled while they drift away. These entangled phosphates then combine separately with calcium ions and oxygen atoms to become Posner molecules, as shown below.
These clusters provide additional “shielding” to the entangled pairs from outside interference so that they can maintain coherence for much longer periods of time over long distances in the brain. When Fisher estimated the coherence time for these molecules, it came out as an incredible 105 seconds – a whole day.12
Although Fisher does not seem to spell out in any detail what happens next – which is important if we want to get the overall picture – this author will try to do so. The numerous entangled nuclei of the phosphorus atoms (within Posner molecules) would be spread out over a wide area in the brain. They would be in a superposed state, existing as waves, for some time before they collapse. When the collapse happens, the electrons in the atom respond. Electrons determine the chemical properties of atoms. So, the collapse causes the chemical properties of the phosphorus atoms to change, resulting in a cascade of chemical reactions which send a cascade of neurotransmitters into the synapses of neurons. The train of electrochemical signals then integrate to form a perception, which is interpreted based on the life-experiences of the person.
This resolves a long-standing question in neuroscience that has baffled scientists: How is the brain able to integrate information from various parts of the brain to form a cohesive perception? Perhaps with “Fisher’s mechanism” (a term that has been freshly minted by this author), a simultaneous collapse of the nuclear spins of entangled phosphorus atoms in various layers and parts of the brain could be the answer.
The most obvious limitation is that currently Fisher’s ideas have not undergone thorough testing, although certain aspects (for example, the longer coherence time of phosphorus atoms) have already been tested in the laboratory. However, there are plans to do so. The first test will be whether Posner molecules exist in extracellular fluids and whether they could be entangled. Fisher proposes testing this in the laboratory by inducing chemical reactions to entangle phosphorus nuclear spins, then pouring the solution into two test tubes and looking for quantum correlations in the light given out.12
Roger Penrose believes that Fisher’s mechanism can only help to explain long-term memory but may not be sufficient to explain consciousness.12 He believes that the Penrose-Hammeroff formulation of microtubules, which he says are more massive than nuclei, is a more robust explanation to this end, although most scientists are skeptical. It would be interesting if Posner molecules (with entangled particles) are found in these microtubules – then both the Fisher and Penrose-Hammeroff hypotheses would be at least partially right. (Everyone likes a happy ending!)
In a Nutshell
1. It has been shown in the laboratory that quantum computing with isolated and shielded phosphorus atoms results in highly accurate results and longer coherence times.
2. Phosphorus is abundant in the brain.
3. The human brain (and perhaps the brains of other animals) may be using the nuclear spins of phosphorus atoms as qubits to carry out quantum computing.
1. Image: Zhang, J. (2019, Sep 28). What Makes Quantum Computing Special? Medium.com.
2. Pla, J., Tan, K., Dehollain, J., Lim, W., Morton, J., Zwanenburg, F., Jamieson, D., Dzurak, A., & Morello, A. (2013). High-fidelity readout and control of a nuclear spin qubit in silicon. Nature, 496(7445), 334-338.
3. Dzurak, A. (2014, Oct 15). Silicon Qubits Could Be the Key to a Quantum Revolution, SciTech Daily.
4. Muhonen, J., Dehollain, J., Laucht, A., Hudson, F., Kalra, R., Sekiguchi, T., Itoh, K., Jamieson, D., McCallum, J., Dzurak, A., & Morello, A. (2014). Storing quantum information for 30 seconds in a nanoelectronic device. Nature Nanotechnology, 9(12), 986-991.
5. Veldhorst, M., Hwang, J., Yang, C., Leenstra, A., de Ronde, B., Dehollain, J., Muhonen, J., Hudson, F., Itoh, K., Morello, A., & Dzurak, A. (2014). An addressable quantum dot qubit with fault-tolerant control-fidelity. Nature Nanotechnology, 9(12), 981-985.
6. Hameroff, S., & Penrose, R. (2014). Consciousness in the universe. Physics of Life Reviews, 11(1), 39-78.
7. Herbschleb, E., Kato, H., Maruyama, Y., Danjo, T., Makino, T., Yamasaki, S., Ohki, I., Hayashi, K., Morishita, H., Fujiwara, M., & Mizuochi, N. (2019). Ultra-long coherence times amongst room-temperature solid-state spins. Nature Communications, 10(1), 3766.
8. Miao, K., Blanton, J., Anderson, C., Bourassa, A., Crook, A., Wolfowicz, G., Abe, H., Ohshima, T., & Awschalom, D. (2020). Universal coherence protection in a solid-state spin qubit. Science, eabc5186.
9. Fisher, M. P. A. (2015). Quantum cognition: The possibility of processing with nuclear spins in the brain. Annals of Physics, 362, 593-602.
10. Fernandes, S. (2018, Mar 27) Are We Quantum Computers? The Current (Science + Technology).
11. Swift, M., Van de Walle, C., & Fisher, M. (2018). Posner molecules: from atomic structure to nuclear spins. Physical Chemistry Chemical Physics, 20(18), 12373-12380.
12. Brooks, M. (2015, Dec 15). Is quantum physics behind your brain’s ability to think? New Scientist.
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