The security of nearly every online transaction today relies on an RSA cryptosystem that could be broken by a quantum computer in around 10 seconds whereas, it takes years of trial and error for a classical computer to try breaking the code and yet, you would still prefer your classical computer as it is still faster than the quantum one for most of your activities. If you aren’t a tad bit curious about it yet? then this isn’t for you.
Our computers have become smaller and more powerful over the centuries. Computer parts are approaching the size of an atom and its becoming a problem. Computers are made up of logic gates which are in turn made up of transistors, a switch that can either block or open the way for the electrons or bits, coming through. These bits are binary in nature, can be set to either 0 or 1. A combination of logic gates form meaningful modules such as, to add two numbers. However, as parts are getting tinier quantum physics is making things trickier.
A typical scale for transistors is 14 nanometers (10^-9 meters) as transistors are shrinking to the size of only a few atoms, electrons may just transfer themselves to the other side of the blocked passage via a process called quantum tunneling, which in-turn makes our computers useless. Some scientists are making use of these unusual quantum properties to their advantage by building quantum computers.
In classical computers bits are the smallest units of information. Quantum computers use qubits which can also be set to any one of the two values. a qubit can be any two level quantum system such as a spin and a magnetic field or a single photon. Some researchers have used the outermost electron in phosphorus as a qubit. When the electron is placed in a magnetic field it aligns to it just like a compass, this is its lowest energy state aka spin down or zero state. You could put it in a one state or spin up but it takes some energy and that is the highest energy state of the qubit. For photons the horizontal and vertical polarization determines its state.
In the quantum world, the qubit state doesn’t have to be in only one of those it could be in any proportion of both states at once, this is called superposition. As soon as you test its value by sending a photon through a filter it has to decide to be either vertically or horizontally polarized so as long as it’s unobserved the qubit is in a superposition of probabilities, much like the Schrodinger’s cat situation. The instant you measure it, it collapses into one of the definitive states.
Superposition is a game changer. Lets take two qubits that exist in a superposition so, they can have the values α x 00, β x 01, γ x 10, δ x 11 where, α, β, γ, δ are four probabilities that could be used to determine the state of this two spin system. Whereas, in a classical system we need only two bits. Hence, two qubits actually contain 4 bits of information. If there were three spins then we would need 8 probability coefficients for each state. Whereas, classical is just 3 bits. If you keep going you’ll find that the amount of equivalent classical information contained in N qubits is 2^N classical bits. Once, we have 300 qubits we have 2³⁰⁰ classical bits which is as many particles as there are in the universe.
A really weird and unintuitive property qubits can have is quantum entanglement, a close connection that makes each of the qubits react to a change in the others state instantaneously no matter how far they are apart. This means when measuring just one entangled qubit, you can directly deduce the properties of its partners without having to look.
A normal logic gate gets a simple set of inputs and produces one definite output. A quantum gate manipulates an input of superpositions, rotates probabilities and produces another superposition as an output.
Essentially, a quantum computer sets up some qubits, applies quantum gates to entangle them and manipulate probabilities then finally measures the outcome, collapsing superpositions to an actual sequence of 0s and 1s. What this means is that you get the entire set of calculations that are possible with your setup all done at the same time. Ultimately, you can only measure one of the results and it’ll only probably be the one you want so you may have to try again. By cleverly exploiting superposition and entanglement this can be exponentially more efficient than would ever be possible on a classical computer.
Quantum computers are not faster but are more efficient in vastly reducing the total number of operations you need to arrive at a result. Hence, they might not replace the ones at your home but in some areas are vastly superior. One of them is database searching, to find something in a database, a normal computer may have to test every single one of its entries. Quantum algorithms need only a square root of that time, which for large databases is a huge difference.
Now lets get to the cryptography part, your browsing, email and banking data is being kept secure by an RSA encryption system in which you give everyone a public key to encode messages that only you can decode, this public key can be used to calculate your secret private key. The math for calculating it consists of the prime factorization of large numbers, doing this math on any normal computer would take years of trial and error but that’s hardly the case with a quantum computer.
Simulations of the quantum world are very intense on resources and even for bigger structures such as molecules they often lack the accuracy so what better way to simulate quantum physics than with actual quantum physics? It could provide new insights on proteins that could revolutionize medicine. In fact, researchers have confirmed that a protein found in bird eyes — the cryptochrome — displays a quantum mechanical phenomenon which makes it sensitive to magnetic fields. This mechanism could be behind a bird’s magnetoreception abilities.
Also, feel free to check out Qiskit, if you are interested in working with quantum computers. It is an open-source software development kit for working with quantum computers at the level of circuits, pulses, and algorithms. We don’t know if quantum computers will just be a very specialized tool or a big revolution for humanity. The quantum is all around us and its time we harness it. I hope I live long enough to see this prodigious quantum revolution.
Video Lecture: Kurzgesagt