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1500 questions
12
votes
1 answer
Evaluating expectation values of operators in Qiskit
I'm wondering how in Qiskit one can calculate the expectation value of an operator given as a WeightedPauli (or, at least, of a single Pauli operator...) in a certain state (given as a QuantumCircuit object — meaning that the actual state is the…
mavzolej
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12
votes
2 answers
Qiskit - Z expectation value from counts?
For a given state $|\psi\rangle$, how would I work out $\langle\psi|Z|\psi\rangle$ ?
If I run a quantum circuit and get the counts dictionary on qiskit, I get observables in the Z basis.
For n=1 qubits, the basis states returned are $|0\rangle$ &…
Zohim Chandani
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11
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1 answer
Travelling salesman problem on quantum computer
Recently a pre-print of article Efficient quantum algorithm for solving travelling salesman problem: An IBM quantum experience appeared. The authors use a phase estimation as a core for their algorithm. This part of the algorithm is used for a…
Martin Vesely
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11
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6 answers
Resources to study quantum algorithms and quantum complexity
I have a computer science background, and I'm interested in studying 'quantum algorithms' and anything that is related like 'quantum complexity'.
I would like to have all important resources that is needed to study quantum algorithms. For example,…
user777
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11
votes
1 answer
What is a flying qubit?
DiVincenzo criteria for quantum communication mentions flying qubits:
a. The ability to interconvert stationary and flying qubits
b. The ability to faithfully transmit flying qubits between specified locations
So, what exactly is a flying qubit, and…
Amitabh Srivastava
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11
votes
2 answers
On the distribution of the fidelity of a random product state with an arbitrary many-qubit state
Consider an arbitrary $n$-qubit state $\lvert \psi \rangle$. How much do we understand about the probability distribution of the fidelity of $\lvert \psi \rangle$ with a tensor product $\lvert \alpha \rangle = \lvert \alpha_1 \rangle \lvert \alpha_2…
Niel de Beaudrap
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11
votes
1 answer
Can quantum computing contribute to the development of artificial intelligence?
I am interested how quantum computing can contribute to the development of artificial intelligence, I did some searching, but could not find much. Does somebody have an idea (or speculations)?
jennifer ruurs
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11
votes
1 answer
Is it possible to run a general implementation Shor's algorithm on a real IBM quantum computer at least for N = 15?
I need to make a general implementation of Shor's algorithm that factors, at least, N = 15. I have been able to perform an implementation that works in simulators, with ProjectQ, but when running it on a real quantum computer.
I have decided to try…
WaSon
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- 4
11
votes
2 answers
Does quantum computing have an essential advantage in analyzing/controlling chaotic systems?
The enthusiast-level, inaccurate knowledge about quantum computers is that they can solve many exponentially solvable problems in polynomial time.
The enthusiast-level, inaccurate knowledge about chaotic systems is that being highly sensitive to…
peterh
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11
votes
4 answers
Grover's algorithm in a nutshell
I am trying to understand Grover's algorithm. I read that this algorithm is able to find an entry in an unsorted list in just $\sqrt N$ steps, and needs only $\log N$ space.
I understand entanglement and superposition, and I also understand most…
Hubert Schölnast
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11
votes
1 answer
Oracle for welded tree walk
There is a famous paper by Childs, et al, in which it is shown that a quantum algorithm can find the name of the exit node for a certain graph in a way that is exponentially faster than any classical algorithm. This speedup assumes an oracle that…
James Wootton
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11
votes
0 answers
Anti-symmetrization on the lattice
Assume, I'm using a system of qubits to simulate a fermionic system.
If I'm using the second-quantized formalism (e.g. orbitals in quantum chemistry), the anti-symmetric nature of the fermionic wave functions can be taken into account by means of…
mavzolej
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11
votes
3 answers
What precisely is the quantum extended Church-Turing thesis?
Context
Prof. Aaronson mentions that the quantum extended Church-Turing (quantum ECT) thesis has no known counterexamples cf. around 14:18 but doesn't mention its precise statement.
Questions
What precisely is the statement of the quantum extended…
Sanchayan Dutta
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11
votes
2 answers
How is it possible to implement unitary operator when its size is exponential in inputs?
A quantum circuit can use any unitary operator. Its matrix is exponential in the number of input bits. In practice how can this ever be possible (aside from operators which are tensor products), i.e. how can you construct exponential size matrix?
John77
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11
votes
2 answers
Submitting jobs to IBMQ backend via HTTP API Requests
Qiskit can be used to submit jobs to IBM devices using Python (or Swift and JavaScript). But what if I want to use a different language?
For example, suppose I have a specific circuit I want to run. Assume I've already created it in Python Qiskit,…
James Wootton
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