Quantum Computer Architecture
The architecture of a computer is the arrangement of its parts: how many subsystems does it have, what does each of the subsystems do, how do the various parts talk …
Course: Understanding Quantum Computers
Superposition and Interference
One of the most important concepts you must grasp to understand quantum computing is the superposition and interference of waves. Since waves are moving through space, you can have more …
Waves
Our first task in learning how quantum computers work is to understand the basic nature of waves. We are all familiar with the waves at the beach and the ripples …
Decoherence
Of course, there is a catch or two to all of this glorious quantum future: perfect quantum computers are very hard to build. Any tiny imperfection in our ability to …
The No-Cloning Theorem in Quantum Computing
Simply put, if you are holding a qubit that is in an unknown state, it is impossible to make a perfect, independent (unentangled) copy of the qubit in all cases. …
Quantum computing: Reversible evolution
In quantum mechanics, every change except measurement (and noise that damages the state, known as decoherence, which we will discuss in the last week when we discuss hardware and quantum …
Measuring Entanglement
When we talked about measuring a single qubit, we described three ways to measure it. They correspond to the X, Y and Z axes on the Bloch sphere we saw …
Entanglement
So far, most of our discussion has involved waves and superposition and interference in ways that are almost entirely classical, except for measurement, and the idea that (n) qubits results …
Quantum Registers: Growing State Space of Multiple Qubits
A quantum computer stores its quantum data in one or more quantum registers. They can store data in quantum superposition, the first key in understanding the advantage of quantum computers. …
Measurement
We just described a single qubit and its important characteristics, its ability to support superposition and phase. But it’s important to note that we can’t directly see either of those …
How to Write down Qubit States
A Point on the Bloch Sphere So far, we have represented our one qubit using two dials, one for the zero state and one for the one state. But it …
Qubits
So far, we have only talked about waves and superposition. We have another half-dozen topics to introduce in our basic concepts of quantum computing, and they are all fundamental physical …
Not Supercomputing, Not Big Data
Quantum computers aren’t suitable for working on problems that involve enormous amounts of data, like climate simulations or what is called “big data”. Let us take a brief look at …
Caveat: Function Growth
How fast does the cost of a function grow? Earlier this week, we talked about the computational class motiviation. In this article and the next, let us add some nuance …
Machine Learning and Other Algorithms
In quantum chemistry, factoring, and generalized search we have seen three of the four important classic (so to speak) algorithms of quantum computing, all developed in the 1990s. (The fourth, …