Real-Life SciFi: Intro to Quantum
Science fiction movies have, and continue to use, insane ideas in plots — like teleportation and walking through walls — since the late 1930s.
They do this with good reason: the craziness of the idea makes it so appealing to watch. Something like that could never be possible in our lives!
The world as we see it works in line with classical physics. The motion of bodies, the interaction of forces on objects and the behaviour of fluids, among other things, dictate technologies used in our daily lives. Supposedly, all that science fiction stuff exists only thanks to our creativity.
Though, the nature of the presence of the laws of classical physics and computing — that govern basically everything we know of and see today — aren’t universal.
Subatomic particles are able to behave in a science fiction state too, according to quantum mechanics.
They have a few superpowers thanks to this, that seems out of a science fiction movie.
Quantum Superposition
Any particle behaving in a quantum state can exist across both a wave state and a point-particle state at the same time (obviously, unlike in classical physics, where some given body takes on one state or the other). Waves are able to overlap in such a state, and individual particles can exist in two places at once.
The rules of quantum physics state that an unobserved photon exists in all possible states simultaneously but, when observed or measured, exhibits only one state. So, this only remains true if a given particle’s energy and position are unknown, allowing for a probability to exist in multiple states. Once we know a particle’s measurements, it’s defined to be in one specific state at a time.
Quantum Entanglement
Two particles are inherently connected and any action or a change in the state of one immediately forces the second particle to change in respect to that same action as on the first particle, no matter how physically separated both particles are.
They usually work in binary, so when one particle takes on one state, the twin particle takes on the opposite.
For example, individual photons can be split into entangled pairs of protons if, say, we shot a laser beam through a kind of crystal. That pair of entangled photons can be separated by any distance, and if Photon A takes on an up-spin state, Photon B, it’s entangled other half, will take on a down-spin state (it’s always in respect to the initial action).
That “communication” of state between Photon A and Photon B takes place at a speed of at least around 10,000 times the speed of light.
In 2019, researchers set up that crystal and laser experiment and took a picture of a pair of entangled photons representing entanglement in opposite states.
Quantum Tunneling
A subatomic particle represented and with characteristics of a wave allows for the said particle to pass through any sort of physical barrier (like an electric field that would otherwise repel a particle or a wall). The idea is, the wave function represents all possible locations of a particle in various locations, giving a probability for that particle to have essentially passed through a barrier in its path.
Quantum Computing
In quantum computing, we can use quantum behaviours, like the powers of entanglement and superposition, to solve increasingly complex mathematical problems faster than classical computers can’t, or take too long, to handle.
Instead of conventional binary bytes, quantum computers use subatomic particles, qubits, to represent data and communicate. It contains both binary options, like ‘0' and ‘1’, but also ‘0 and 1’. Meaning, a qubit can represent both options at once; they harness the power of superposition to do so.
Some of the hardest mathematical problems to solve in a real-world context are those involving optimization across various ‘paths’ of achieving an end goal. A classical computer needs to explore every possible option to determine which set of actions leads to the end goal of a program in the most efficient way.
But thanks to qubits, a quantum computer can explore all options of a complex optimization problem by manipulating the permutations of variables at the same time to find the best path. There is an exponential decrease in the time taken to reach a conclusion.
Here’s a great example my friend Tanisha uses.
A person writes an X on a random page in a random book in a library with 1 million books and tells a quantum and classical computer to find the X. For a classical computer, it would have to sort through every page of every book one by one to find the X which would consume a lot of time. For a quantum computer, a qubit in superposition can be in multiple places at once so it can analyze every page at the same time and find the X instantly.
Now imagine that level of speed and performance enhancement when it comes to exploring chemical combinations in designing drugs or experimenting with various elements and compounds in optimizing a material's photovoltaic effect efficiency.
The optimization problem is the prime target of quantum computing technology because classical computing would take exponentially longer to explore all possible permutations and combinations.
The ability of a quantum computer to be in many places at once is an incredible enhancement to computing; we can solve complex problems effectively, that we previously never imagined we could.
Running Quantum Algorithms and Computers
To get a quantum algorithm working, we first need an operational quantum computer. First, we initialize all of your qubits to a known state, rotate and measure individual qubits and perform an operation that entangles pairs of qubits. We have to make sure to stay free of outside interference (called decoherence) for as long as possible to let the computer finish its quantum processes.
When implementing a quantum algorithm in a system, we need to activate qubits to reach superposition in all possible states, encode the optimization problem by applying a phase on each superposition state and then use methods of constructive and destructive interference to ‘cancel’ or add phases to optimize for the correct answer and shrink the wrong answers (almost like tweaking the system with specific actions to indicate desired and undesired results).
We have to be careful when it comes to scaling the system to a larger number of data points and variations, as we face higher error rates as more qubits are added to a system.
For a quantum computer to be functional it must have qubits that can harness quantum properties; since qubits are prone to instability and error, we run our system at temperatures close to 0-kelvin degrees to minimize error rates.
When using a quantum computer for a specific problem-solving task becomes more effective than using a classical computer, it’s called to have reached quantum supremacy. Google recently achieved this in 2019, and it serves as a strong boost of confidence for the great impact quantum computers can have on solving problems in society.
Types of Qubits used in Computers Today:
Cheers,
Swarit.
