How Does a Quantum Computer Work?
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a starting point for newcomers asking how quantum computers work, and as the source of confusion in questions about qubits and measurement.
Recommended by 1 people across 1 different months, 2015 to 2020.
What it is
A short Veritasium explainer, made with UNSW physicist Andrea Morello, on how a quantum computer differs from a classical one. It introduces qubits in superposition, notes that N qubits need 2^N numbers to describe, and says measurement forces a collapse into one basis state.
Cited in 1 Wikipedia article, including Andrea Morello.
What people said
Recommends Jaywalker · 2016-03 · Physics Stack Exchange · on “How do Quantum Computers work?”
There are some interesting videos on quantum computing by a number of quite serious youtube channels. This is a good place to start: [this video]
Cites Tejas Ramdas · 2015-04 · Physics Stack Exchange · on “An analogy for qubits and quantum computing?”
I have understood that qubits are special ways to store data where they exist in more than the conventional 2 states. However, I do not understand how they are read, interpreted and manipulated despite reading quite a few articles. Is there possibly a good analogy to explain how they can potentially speed up calculations? There is also a video on youtube by Veritasium [this video] where they explain why it is not necessary that quantum computers reach an answer more quickly as compared to conventional ones? Could somebody throw some light on that too?
Cites user182786 · 2018-01 · Physics Stack Exchange · on “Which set of basis states can a quantum system of qubits actually collapse to?”
I was watching a video on " How Does a Quantum Computer Work? [this video] ". I'm confused about what they mean by: " Although the qubits can exist in any combination of states, when they are measured they must fall into one of the basis states. " From what I know about linear algebra, if we represent the state of a qubit by $|\psi\rangle$ it can be written like $\alpha|x\rangle + \beta |y\rangle$ (where $|x\rangle$ and $|y\rangle$ form a basis) or $\gamma (|x\rangle+|y\rangle) + \delta (|x\rangle-|y\rangle)$ or even $A(|x\rangle+|100y\rangle) + B |y\rangle$! What I mean is that no set of basis states is unique . So, in reality which set of basis states can a qubit (or more generally a quantum sy
Cites Christoph · 2020-01 · Physics Stack Exchange · on “Understanding bra-ket notation as in quantum computer in terms of pure algebra”
Are $-|0\rangle$ , $i|0\rangle$ , $\frac{1+i}{\sqrt2}|0\rangle$ valid (that is, physically possible) kets? How are they different from $|0\rangle$ ? Yes, they are valid, but describe the same physical state. A state can be characterized by its expectation values, and a phase factor $e^{i\varphi}$ cancels with the complex-conjugate factor from the bra. Technically, (pure) quantum states don't live in the Hilbert space, but its projective space. Note that such phase factors do matter when superposing states: While $+|1\rangle$ and $-|1\rangle$ describe the same state, $$ \frac{1}{\sqrt2}(|0\rangle + |1\rangle) $$ and $$ \frac{1}{\sqrt2}(|0\rangle - |1\rangle) $$ do not. Do $|00\rangle$ , $|01\
Cites Luke · 2020-01 · Physics Stack Exchange · on “How does QC work?”
I watched this video [this video] That says QC has 2 to the N bits. And that is somehow useful. But they don’t say why lots of bits can be useful. Can anyone please explain how it works in simple terms?
Cites Dannyu NDos · 2020-01 · Physics Stack Exchange · on “Understanding bra-ket notation as in quantum computer in terms of pure algebra”
Since I'm not a Physics student, but a Mathematics student, the only physics course I went through is elementary physics (일반물리학, textbook by Jearl Walker, David Halliday, and Robert Resnick). Not even Classical Mechanics. Yet, I've been interested in quantum computing, and my professor (who is an expert in Analysis and Image Processing) recommended me a book, Practical Quantum Computing for Developers by Vladimir Silva. As a consequence, I had to understand bra-ket notation. Past glances (Wikipedia, Youtube videos, and applets by Paul Falstad [LINK] ) to Quantum Mechanics didn't much help, yet other questions here were helpful. As far as I understand: Kets are unit vectors in a function spac