Can Particles be in Two Places at Once? The Weird Quantum Superposition
What if I say that there is another variant of yours somewhere in the timeline? What if the science fiction we watch in the Marvel series named Loki does exist? 😵 Some things in quantum mechanics seem very strange. Is it possible that the same object can be in different places? Not one after another but at the same time? 😮 If yes, then why don’t we see it in everyday life (classical world)? The answer is simple, a quantum system requires a very specialized environment and when it gets measured, it is so sensitive that it comes out of it and collapses to one state.
In Simple Words
A concept in quantum mechanics describes that an object can be in multiple states at the same time until they are measured while in a classical system, there is one well-defined state at a given time.
So, the electrons, photons, or atoms can exist in more than 1 location simultaneously at least until the measurement is made i.e. something can be “up” and “down” at the same time.
During superposition, particles having different states can be rethought as the different outcomes with the probability observed. Once measured, the quantum system collapses into one state. These states are referred to as “wave function” which are combined through superposition and on measurement collapse into a single state. We’ll get to know more about wave function later.
Mathematical representation
In easy terms, something that has more than 1 solution for an equation. Eg, x² = 9 where x=-3 and x=3.
- Superposition is the combination of all possible states in the Herbert space before it collapses to one state during the measurement of a quantum system.
- The nature of the outcome is always probabilistic, unlike classical physics. There we have a determined solution but here it’s always a probability value of a particular thing to happen. This value is calculated using the wavefunction.
- Wave function represents a quantum state which contains information about the particle’s position, momentum, and other observable properties. The square of the absolute value of the wavefunction (|Ψ|²) gives the probability density of finding a particle at a specific location.
Superposed wave equation, |ψ⟩ = α |ψ1⟩ + β |ψ2⟩
where
|ψ⟩ : Qubit state,
(α,β): complex numbers,
(|α|²,|β|²): probability amplitude for finding system in states (ψ1,ψ2) respectively.
Hence, the qubit state of 0 and 1 i.e. |ψ⟩ = α|0⟩ + β|1⟩
In Figure 1, Qubit has 0 (spin down) and 1 (spin up) as 2 possible options for spin direction at the same time.
What happens on measurement?
Before we measure(observe) the system, it’s in a superposition state that is in multiple different states at the same time. When we measure, superposition collapses into one well-defined state giving us the illusion of always one state in our classical world. This well-defined one has concluded with the squared magnitude of coefficients i.e. probability of each state.
How does Quantum Computer leverage Superposition?
Quantum Computer has quantum gates which create and manipulate the superpositions of states. This sounds a bit strange and interesting. But similar to logic gates and circuits, we have quantum gates and quantum circuits in quantum mechanics.
The superposition property of qubits is what gave the power of exponential parallelism to Quantum Computers. Quantum parallelism provides exponential speedup than classical computers.
There are other such Quantum Mechanics concepts such as entanglement and interference which I will be covering soon in the later blogs. Till then, try to think if you could also have your variant somewhere. 😉
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Happy Learning! 😄
