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Newest 'quantum-state' Questions - Quantum Computing Stack Exchange
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Learn more about TeamsQuestions tagged [quantum-state]
Questions about or related to quantum states. Consider using the density-matrix tag when relevant.
1,828 questions
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Creating T gadgets
Consider an arbitrary Clifford circuit, terminating in a last layer of $T$ gates. Is it possible to construct a $T$ gadget using post selection in this setup?
If we have $T$ gates in the beginning, ...
2
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1
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70
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How to transform the density matrix from one basis to another basis
Suppose I have a density matrix for 2 qubits which is 4 by 4, in $Z$ basis $\left(|0\rangle,|1\rangle\right)$. Now I want to transform the density matrix to $X$ basis $\left(|+\rangle,|-\rangle\right)$...
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Maximally complex states
In terms of gate count, Haar random states are maximally complex. If we yet consider (mixed) states, how can we characterise states with maximal complexity?
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Question about tracing out one subsystem when two qubits are entangled
I encountered one question when preparing for the exam.
(b) Suppose each of the qubits of the state $|\phi^+\rangle_{AB}$ undergoes a decoherence process of the form
$$
\rho \mapsto e^{-t} \rho + (1 - ...
3
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2
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278
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How would a DiVincenzo machine prepare the maximally mixed state with a small number of ancilla qubits?
For a while I had been thinking that the maximally mixed state is a problematic or pathological state not useful in quantum computing, insofar as it corresponds to a completely decohered state while ...
2
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1
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54
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Infinitesimal trace distance and metric
It is well known that the Bures distance between two infinitesimally close density matrices induces the Bures metric. Likewise the quantum Fisher information metric is related to the infinitesimal ...
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37
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Could metronome synchronization entangle multiple qubits simultaneously? [closed]
Could some eventually consistent medium be used to entangle lots of qubits simultaneously?
I'm very much a novice, but I'm thinking something like metronome synchronization on a skateboard. Arrange a ...
1
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1
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128
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Low Fidelity For QFT on IBM
I implemented a 5-qubit QFT circuit using Qiskit and performed quantum state tomography using an IBM backend. However, the reported process fidelity is only ~20%, which seems very low. I am trying to ...
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41
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connection between no-cloning theorem and accessible information
In the following paragraph Nielsen and Chuang give proof (with contradiction) that no-cloning theorem about non-orthogonal states lead to accessible information will be less than $H(p)$.
BUT no-...
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1
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107
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Advantages of using qubits for data storage
I have read much of the book Quantum Computation and Quantum Information by Nielsen and Chuang and I of course have been convinced that qubits have great advantages in many problems when we want to do ...
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Encoding circuit from Stabilizers and Logical operators stim
Given that I provide stim the stabilizer generators and the logical operator specifying the logical state that I want to encode (starting from the all 0 state), does something like
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applying Haar random unitary to projection and pure states and compute its trace
I have this question when I read the proof of Theorem 4 in This paper. Here are the settings:
\begin{align}
&|\phi\rangle^{BC}: \text{The reduction of a pure state $|\phi\rangle^{ABCD}$ where A,C ...
2
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174
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Question about a Haar random state
Let's consider a Haar random state on $n$ qubits. We trace one qubit out. Can we prove that the reduced density matrix that remains is "close" to a convex combination of two Haar random ...
2
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1
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183
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Why would we need 512 classical bits to represent a two-qubit entangled state?
I am new to quantum computing. I see a claim in a video from IBM Research that $2$ qubits needs $512$ classical bits to represent an entangled state. I would like to understand where this comes from.
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Proof of Theorem 3 of Frenkel, and Weiner, Commun. Math. Phys. 340, 563 (2015)
Suppose Bob performs a $k$-outcome measurement, characterised by the POVM $E = \{E_j\}_{j=1}^k$, on $l$ qudits $\{\rho_i\}_{i=1}^l$ sent by Alice. This results in an $k \times l$ column-stochatstic ...
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Related Tags
quantum-gate × 367
entanglement × 300
measurement × 193
qiskit × 192
linear-algebra × 178
textbook-and-exercises × 173
density-matrix × 154
programming × 150
quantum-algorithms × 126
circuit-construction × 92
bloch-sphere × 83
quantum-circuit × 69
quantum-operation × 66
unitarity × 53
superposition × 51
information-theory × 50
ibm-q-experience × 50
nielsen-and-chuang × 46
probability × 46
error-correction × 38
fidelity × 38
haar-distribution × 35
simulation × 34
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