What you need to know about the next computer revolution. Quantum Mechanics (Part V)
Quantum Computers Explained
This is the fifth part of my series.
Here are the goals of this series of posts:
1. Outline the major events that formed this branch of physics
2. Describe in, simple words, the fundamental main ideas of Quantum Mechanics
3. Understand the essence of quantum computing (full focus)
4. Understand aspects of current research into quantum technologies
Here’s an overview of my series of posts on Quantum Mechanics. I’ll publish these once a week beginning on the 12th of August.
1. The Historical Beginnings
2. James Bond teaches you uncertainty, entanglement, and interference
3. What is the probability that you’ll learn a bit about probability, quantum computing, qubit, polarization, and psi? 100%!
4. If Quantum Physics is Real, is Reality Real? What Jaden Smith didn’t tell you about the reality of our world (and the quantum physics of what’s real)
5. What is a quantum computer? A (fuller) introduction to Quantum Computing (this one right here)
6. Ongoing Quantum Research #1 (quantum semi-conductors and you)
QUANTUM MECHANICS PART V
Computer scientist Rolf Landauer once mentioned that “information is physical,” which, if so, means information could very well be categorized, handled, and physically supported by quantum mechanics.
Two types of computers that I would like to mention are: classical computers and quantum computers.
Classical computers (the things we use to read this post right now) are powered by logic gates, which allow for a transfer of electricity to generate binary signals. Classical computers are noteworthy however for they are without any true moving parts that distinguished the first iterations of computers and are instead the result of ingenuity in electrical circuitry.
Quantum computers will rely on quantum physics. Quantum states will encode most of the information on these computers. And, most excitingly, quantum computers can process information at rates much faster than typical classical computers. With an addition of each storage unit (the qubit), information processing can be completed at a rate of 2^n. If each computation takes 1 second, and when n is equal to 32 then:
2³² = over four billion computations to be done
Using a classical computer, it would take a little over 32 years to calculate. Using a quantum computer, it would take one second (source: Ahn-Park, 2011, Engineering Quantum Mechanics).
If you are an individual seeking to analyze what the best way to create a anti-viral drug, quantum computers are the next big step forward. If you have to run through thousands of passwords to break an RSA encryption, quantum computers are again the next big step forward. Quantum Computers will move humanity a hundred thousand times forward.
So How Do Quantum Computers Truly Differ From Classical Computers?
Besides quantum processing speeds, there are some huge structural differences in a quantum computer.
In a classical computer, information, is a previously mentioned in a previous post, encoded by a bit. For example, a classical computer reads the collection of 0’s and 1’s in “00110001” to produce the number “1”. But a quantum computer can use the ideas of superposition and entanglement to help go beyond 0s and 1s. Furthermore, quantum computers must be reversible (i.e. information never being lost). Classical computers lose information as they are irreversible. This is something that a classical computer can’t do. So, with a quantum computer, it can have a qubit having a superposition state of both 0 and 1 at the same time.
How?
Through superposition, however, this is structurally achieved by quantum logic gates.
Logic gates? What’s that? Computers depend on logic gates to turn information from inputs to outputs.
With my own oversimplification, one puts something into the computer (input of a keystroke of 1’s and 0's) and as a result, the computer spits out the resulting output whether it be to turn on a piece of a display or give us a letter.
Likewise, in quantum computing, there are also logic gates. Two types I should mention are the Controlled-NOT gate (also known as the XOR, or known as the Quantum XOR, or the measurement gate) and the Hadamard Gate.
A Controlled-NOT Gate
In essence, a Controlled-NOT gate makes an entanglement output if given an superposition state in the input.
You give it two inputs:
A Qubit of Quantum State of 0 be it related to spin, polarization of photon, etc.
A Qubit of Quantum State of 1 and 0 (superposition) be it related to spin, polarization of photon, etc.
==> what you get out:
One output:
A Qubit of Quantum State (0) with superposition of Quantum State (1) plus A Qubit of Quantum State (1) with superposition of Quantum State (0)
Hadamard Gate
A Hadamard Gate only acts on one qubit (thus has one input). From one input:
A Qubit of Quantum State 0
==> what you get out:
A superposition of (0) and (1) qubit states. And since a superposition will collapse to form one state, and according to Born’s rule that there is equal probability of observing one or the other state, scientists can allow quantum computers to work with more outputs (up to size 4) from just one input. And, without going into the math of it, even though there is 4 outputs and 1 input, this process is completely reversible such that if you know the output, you know the input.
Scientists have found out that through various combinations of different types of quantum gates, one can have a basis for a quantum computer.
Next Steps
So after quantum states and quantum information are inputted into the first of the quantum gates, the output has entered into a quantum processor. Here, in this quantum processor, more quantum gates act upon the previous quantum gates, until this ping-pong ball machine of beeps and blurps (that’s how I visualize it) give us an output that is in entangled state.
And throughout the whole process that it is in a ping-pong ball machine of quantum gates, it has to be continuously held in a state of superposition. To stabilize these qubits at a superposition, they must be cold. Very cold. -273 degrees Celsius cold.
And the output —it’s in an entangled state …
Wait — really? The output is entangled? But how do we know what the result is then?
After the calculation is over and the superpositions are no longer, under observation, the quantum computer would spit out a measurement. It very well could be a random one in accordance to Born’s rule.
So, we add another step here: scientists would have an error correction stage using an algorithm just before they store the Qubits in memory. Once error corrected, the randomness factor has been removed and the quantum result has been achieved.
So that’s how a quantum computer works at the fundamental qubit gate level! Hope it helps!
