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1500 questions
6
votes
2 answers
Quantum counting in Q#
I cannot seem to get an estimate for the number of solutions using the quantum counting algorithm described in Nielsen and Chuang, i.e. phase estimation with the Grover iteration acting as $U$.
I try doing the following with control and target as…
nikojpapa
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6
votes
3 answers
Controlling high-dimensional Hilbert spaces with a single qubit
In superdense coding, you can use one qubit to control the Hilbert space of two qubits and steer it into 4 mutually orthogonal states, so that measurement of both qubits together will not have a probabilistic outcome.
I think the idea is cool. I…
psitae
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6
votes
1 answer
Is there any single-logical-qubit physical device out there as of end 2018?
By my first impression, there are many-qubits computers out there and more to come, as to follow the press.
Now a closer look reveals that it's all about designing and building physical qubits.
Then, as it seems from further reading, you actually…
J. Doe
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6
votes
2 answers
Balanced vs unbalanced superposition distinguisher
I've been looking at basic quantum algorithms such as the Deutsch-Jozsa algorithm that are able to characterize functions very well and I was wondering if similar approaches exist to characterize quantum states.
Consider the following example: Given…
user1936752
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6
votes
2 answers
Why is super-dense coding called the inverse of quantum teleportation?
I am new to quantum computation and I recently came across the statement that super-dense coding can be called the inverse of quantum teleportation
Aleph
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6
votes
2 answers
BB84 attack with entangled qubits example
BB84 attack with entangled qubits example
Hi, I'am interested in an attack for BB84 protocol with entangled quibits.
Lets say Alice sends a qubit $x$ in state $\left|1\right>_x$ to Bob and Eve takes the CNOT gate to
entangle the states. Therefore,…
user4961
6
votes
1 answer
Why is the $N$-qubit stabilizer group abelian?
In Devitt et al. 2013's introduction to quantum error correction, the authors mention (bottom of page 12) how the stabilizer group for $N$ qubits is abelian.
More specifically, here is the quote:
An $N$-qubit stabilizer state $\lvert\psi\rangle_N$…
glS
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6
votes
1 answer
Can we use quantum machines to reduce space complexity of deterministic turing machines?
Can we convert every algorithm in $\text{P}$ (polynomial time complexity for deterministic machines) into a quantum algorithm with polynomial time and $O(\log n)$ quantum bit?
Mohsen Ghorbani
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6
votes
0 answers
Discrepancy regarding Husimi Probability distribution
I am trying to simulate a system of j qubits and for visualization of the dynamics considering the Husimi distribution of the state.
To carry out the projection onto coherent states I have proceeded in the following manner
…
Sudheesh
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6
votes
2 answers
Do the probability amplitudes of the superposition state produced by the QFT transform convey useful information?
I have been studying on Quantum Fourier Transform (QFT) by myself, and I am little bit confused about how could QFT be used.
For example, if the QFT of three quantum bits is
$a_1|000\rangle + a_2|001\rangle + a_3|010\rangle + a_4|011\rangle +…
Emma
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6
votes
1 answer
Understanding the growth step of the magic state cultivation protocol
I'm having trouble following the description of the growth phase in the magic state cultivation protocol from Gidney2024. I would really appreciate a more detailed explanation of what's happening in Figure 9 of Gidney2024. In particular,
Do the…
BarryVu
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6
votes
1 answer
What's the longest period that an $n$-qubit Clifford operation can have?
In https://arxiv.org/abs/2506.15147 , high-period constant-depth Cliffords are used to catalyze Z rotations. For an $n$ qubit state, the paper uses a Clifford with period $2^n-1$ built entirely out of CNOT gates.
Ignoring the constant depth…
Craig Gidney
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6
votes
0 answers
Low entropy implies far from maximally mixed
A paper I've been reading (1, just after eq. 5.1) claims that if $\rho$ is a quantum state on $n$ qubits, and $S(\rho) \le (1 - \epsilon)n$, then $$\|\rho - \tilde{I}\|_{\text{tr}} \ge \epsilon - \frac{1}{2^n},$$ where $S$ is the von Neumann…
user68775
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6
votes
1 answer
Lattice based cryptography vs BB84
Am I correct in thinking that post-quantum cryptography such as lattice-based solutions run on classical computers are resistant to quantum attacks (as opposed to RMS), whereas quantum key distribution schemes such as the BB84 are designed to run on…
Matthew Giles
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6
votes
1 answer
Quantum Algorithm for MIMO ML detection
I am reding the paper EXIT-Chart Aided Near-Capacity Quantum Turbo Code Design by Babar et al. and in the introduction, it is stated that due to the exponentially increasing complexity of the MIMO ML decoding, it is an idea to pass such problem to…
Josu Etxezarreta Martinez
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