British astronomer, physicist, and mathematician, Sir Arthur S. Eddington put forth the concept of the “time’s arrow” in the 1920’s . Eddington theorized that time is asymmetrical, and moves in one direction from the irreversible past to the present, then forward towards the future. He proposed that the reason why time moves forward is due to causal asymmetry (cause and effect). Does this arrow of time hold true in quantum computing?
In classical computing, information is stored in bits with discrete binary values of either a “1” or “0.” In contrast, in quantum computing, information is stored in quantum bits (qubits) which can not only have the states of “1” or “0,” but also be in superposition of these states – where any two or more quantum states can be superposed (added together), resulting in another valid quantum state.
To visualize a qubit, think of a sphere. The Bloch sphere is a geometric model of a qubit where any point on the surface represents a pure qubit, and points inside the sphere represent mixed qubit states.
A single qubit can be a linear combination of |0⟩ and|1⟩, where |ψ⟩=α |0⟩ + β |1⟩, and α and β are probability amplitudes that can both be complex numbers.
A global team of researchers from the National University of Singapore, the University of California at Davis, the University of Oxford, Nanyang Technological University, and the Austrian Academy of Sciences, discovered that quantum computing is less bound to the arrow of time and published their findings in a scientific paper titled “Causal Asymmetry in a Quantum World” in Physical Review X in July 2018 .
The scientists measured the amount of memory overhead incurred when modeling a stochastic process in one temporal order versus another in both classical and quantum models. The team discovered that quantum models “forced to run in the less-natural temporal direction not only surpass their optimal classical counterparts but also any classical model running in reverse time.”
The scientists demonstrated that “classical favoritism for particular causal orders vanishes when quantum models are permitted, thus highlighting a new mechanism for the origin of time’s arrow.” What remains to be determined is whether or not cause and effect exists in any quantum models.
Many physicists posit that time have been moving forward since the beginning of the universe with the Big Bang 13.7 billion years ago. Will the advent of quantum computing redefine our understanding of the arrow of time?
Copyright © 2018 Cami Rosso All rights reserved.
1. Billings, Lee. “2 Futures Can Explain Time’s Mysterious Past.” Scientific American. December 8, 2014.
2. Thompson, Jayne; Garner, Andrew J.P.; Mahoney, John R.; Crutchfield, James P.; Vedral, Vlatko; Gu, Mile. “Causal Asymmetry in a Quantum World.” Physical Review X. 18 July 2018.