For questions about the usage of, origin of or reasons for specific notation used in the context of quantum computing.
Questions tagged [terminology-and-notation]
190 questions
46
votes
5 answers
How does bra-ket notation work?
Quantum algorithms frequently use bra-ket notation in their description. What do all of these brackets and vertical lines mean? For example: $|ψ⟩=α|0⟩+β|1⟩$
While this is arguably a question about mathematics, this type of notation appears to be…
Ella Rose
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2 answers
What counts as an "ancilla" qubit?
I am getting confused about the meaning of the term "ancilla" qubit. It's use seems to vary a lot in different situations. I have read (in numerous places) that an ancilla is a constant input - but in nearly all of the algorithms I know (Simion's,…
Quantum spaghettification
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Is qsphere an actual term representing 5 qubits?
I'm a total beginner, I've been brought here by the featured stackoverflow blog post so I started studying.
Watching this youtube video (A Beginner’s Guide To Quantum Computing (3:58), I saw this slide where it talks about superposition:
At first I…
Adelin
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7
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1 answer
Elementary question: is $\langle a|b \rangle$ the same as $\langle a||b\rangle$?
In trying to learn more about quantum computing, one of the first things encountered is a definition of the inner product $\langle a|b\rangle$. If I interpret it correctly, and looking near the bottom of page 15 of the 2011 book by Rieffel and…
mhucka
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6
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3 answers
What is meant with "shot" in quantum computation?
What is a "shot" in relation to quantum computing? I heard it is repeating time, but I don't understand it. Additionally, why is the default number of shots 1,024 in the IBM Q Experience?
One more question - I saw the sentence for each value of the…
김동민
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5
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2 answers
What does it mean that 1 qubit can do the job of 1 ebit (entanglement bit)? (second Bennett's law)
I just came across Bennett's laws and I wonder what the second law mean. It states that 1 qubit "can do the job" of 1 ebit. However, the definition of ebit (entanglement bit, wiki just refers it to the Bell state) and the notion of "can do the job"…
Fallen Apart
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4
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2 answers
Why is the word amplitude used in quantum computing?
Apparently no one has asked why the word "amplitude" is used to refer to the complex numbers that determine the probability of a quantum object to be found in a certain state. The word amplitude to me means the distance between the lowest point on…
user1145880
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What's a nice, intuitive notation for indicating that two operators can or should be run in parallel?
Suppose I have a unitary operator acting on a state $|\psi\rangle$, such as:
$$\big (\sqrt A\sqrt B\sqrt C\sqrt D\big)|\psi\rangle.$$
Conventionally, $\sqrt D$ is performed first, then $\sqrt C$, then $\sqrt B$, and finally $\sqrt A$, i.e., the…
Mark Spinelli
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4
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Is there any standard notation for two states being "equivalent up to a global phase"?
Is there any standard notation for two states "equivalent up to a global phase"?
Currently, I use just an equal sign but I'd like to use a different symbol to distinguish between two phases that are exactly the same (equal sign) and two phases which…
Flipper
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4
votes
2 answers
Why do we say 'classical computer' to mean 'digital computer'?
The term 'classical computer' is always used to mean standard digital computation (Turing model, Boolean circuits or just good old RAM). I have never seen it to mean other models of computation based on classical physics (such as analog…
James Wootton
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4
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1 answer
How should I understand the link between $x$ and $| x \rangle $?
In the paper "Quantum Expectation-Maximization for Gaussian Mixture Models" I encountered the following proposition :
Consider two vectors x,y and $\theta$ the angle between x and y, $\theta < \frac{\pi}{2}$. Then $||x - y|| \leq \epsilon$ implies…
nathan raynal
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3
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Notation question: How would one read $|0\rangle (|0\rangle+|0\rangle)$?
For example in Deutsch's Algorithm, we apply $H$ to $|0\rangle$ and $|1\rangle$ respectively. I have seen the notation this result in the state:
$$\frac{1}{2}(|0\rangle+|1\rangle)(|0\rangle-|1\rangle)$$
However, it is unclear to me how exactly I…
csstundent
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3
votes
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Which unicode character should be used for the angle brackets in braket notation?
When the use of LaTeX or MathJax or other typesetting system is not an option, one can still type the braket notation $\left<\psi\right|$ and $\left|\psi\right>$. The simplest way is probably to use the plain "less than" and "greater than"…
mhucka
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3
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Terminology: quantum state vs. quantum system vs. qubit
What are the difference between quantum state, quantum system and qubit(s)?
M. Al Jumaily
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What does $\lvert \psi \rangle$ mean?
What does the notation $|\psi\rangle$ mean and how does it relate to the notation $|0\rangle$ and $|1\rangle$? Does $\psi$ have some connection to the one found in Shroedinger's equation?
develarist
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