Quantum Computing sounds like a term straight out of a science fiction novel. But after the initial wave of awe at this buzzword, most people are left wondering, “so what does actually mean?”
Let me tell you! Scroll down to see this emerging field’s purpose, physics/hardware, progress, and potential.
Classical computers have come a long way since its inception. Running on binary values of 1s and 0s, these computers are able to perform the great feats we take for granted, like play videos, store information, run applications, and much more. While classical computers are useful for many purposes, there are areas where these computers miserably fail, like simulating molecules and proteins, optimizing, and generally processing large amounts of data in parallel.
Quantum computing runs on a fundamentally different system, storing information in qubits (quantum bits) that are in a superposition of any state between 0 and 1 rather than a singular value. Once this state is measured, it collapses into a singular state of 0 or 1.
What this means is two qubits have four possible configurations, three qubits have eight possible configurations, and so on. In other words, the possible states of N qubits is 2^N. This exponential scaling is unimaginable. 300 qubits contain 2³⁰⁰ bits of information in parallel, which is the number of particles in the universe.
Qubits can also be entangled, which means the state of one qubit is linked to that of another, so once we measure the state of one qubit, we know the state of the other one. Using these two properties, we can cleverly arrange a circuit of quantum gates to manipulate, entangle, and measure the superposition of qubits to eventually collapse into a sequence of 0s and 1s, which represent the final answer. The beauty of this process is that multiple states are calculated simultaneously before giving an answer, so for problems with many possible configurations of answers, quantum computing is exceptionally powerful.
Physics and Hardware
I mentioned entanglement and superposition in the description above, but let’s delve deeper into what those properties mean. In the twentieth century, humans discovered that everything in the universe has a wave particle duality. All of the physical objects you see to the smallest of particles can be represented as a wave function, encompassing all of its potential states of existence. As you go down to the subatomic level, you notice that the line between wave and particle is more blurred; we can not predict with absolute certainty where in the universe an electron will be present and what its momentum will be. This information is in a black box, because the electron is in a superposition of many states, represented by its wave function. Once we try to measure it or if it experiences decoherence, it “collapses” into a deterministic state. When the waves of two or more particles meet, they can constructively or destructively interfere, much like how two waves in the ocean can pile on top of eachother or cancel each other out. When this happens, the waves of the electrons are entangled, and become one individual wave. This links the state of one electron with the other one, regardless of the distance between the particles.
A qubit can be any simple quantum mechanical system with two possible states, such as an electron with spin up or down, or a photon with a vertical or horizontal polarization.
In order to effectively measure these systems, we need to be able to measure the energy difference between the two possible states and ensure that it is larger than the thermal energy of the environment. Let me use the electron for an example. The energy of the up and down spins of an electron is proportional to the magnetic field that it is interacting with. In order to achieve a significant energy difference, the magnetic field on the electron must be strong and the temperature of the environment must be extremely low (close to 0 degrees Kelvin, or absolute zero). To control the state of the electron’s spins, high frequency magnetic resonance, which produces strong magnetic fields, is also needed. Finally, the voltages of miniscule electrodes would control bonds between qubits and allow them to interact.
The result is this:
A lot of huge companies are investing heavily on quantum computing research because of its startling potential. IBM has created the first commercial quantum computer, which is accessible to the public through their cloud based platform Qiskit. Google is also conducting quantum computing research, and achieved quantum supremacy in 2019 when its Sycamore quantum computer beat the task of solving a random sampling problem in only a few minutes, while its classical computer would have taken 10,000 years (this number is disputed, but either way it is still a huge accomplishment). Even governments are hopping on the technology — the US Government is investing $1.2 billion in quantum information sciences over the next five years, and China is building a multibillion dollar National Laboratory for Quantum Information Sciences and funding a large quantum computing project expected to achieve major breakthroughs by 2030.
Quantum computing is like the lightbulb of computing. Its potential is incredible, and I’m excited to live through these exciting times!