Most Popular
1500 questions
9
votes
1 answer
Is it possible to speed up the generation of the weighting matrix using a quantum algorithm?
In this[1] paper, on page 2, they mention that they are generating the weighting matrix as follows:
$$W = \frac{1}{Md}[\sum_{m=1}^{m=M} \mathbf{x}^{(m)}\left(\mathbf{x}^{(m)}\right)^{T}] - \frac{\Bbb I_d}{d}$$
where $\mathbf{x}^{(m)}$'s are the…
Sanchayan Dutta
- 17,945
- 8
- 50
- 112
9
votes
2 answers
How to implement Projector Control-Not in Qiskit?
I want to impliment Projector Control-Not in Qiskit just like in this , which is a $|0\rangle\langle 0|$ projector found in the paper "Grand Unification of Quantum Algorithm" page 7. Also, is the angle $\phi$ and the exp same as the parameter of…
Shashi Kumar
- 419
- 2
- 8
9
votes
1 answer
How to find a density matrix of a qubit?
If we are given a state of a qubit, how do we construct its density matrix?
PiMan
- 2,235
- 1
- 21
- 32
9
votes
1 answer
Can quantum annealing find excited states?
If we start with a Hamiltonian $H(t_i)$, and with our qubits prepared in the ground state of this, and then slowly change this to a Hamiltonian $H(t_i)$, the final state of our qubits should be the ground state of the new Hamiltonian. This is due to…
James Wootton
- 11,700
- 1
- 35
- 74
9
votes
1 answer
What is the applicability of quantum network coding?
As the title suggests, I want to know what the applicability of quantum network coding is, besides the EPR pair construction between distant pairs of 'Users-Targets'.
Can quantum network coding be used for computation?
Ivanovitch
- 673
- 1
- 6
- 7
9
votes
3 answers
How to implement the "Square root of Swap gate" on the IBM Q (composer)?
I would like to simulate a quantum algorithm where one of the steps is "Square root of Swap gate" between 2 qubits.
How can I implement this step using the IBM composer?
JanVdA
- 1,158
- 1
- 8
- 17
9
votes
1 answer
Where can I find example circuits to learn from?
I'm relatively new to quantum computing and my goal is to learn how to implement algorithms that I read in papers. While I have found many circuit snippets I have yet to find a repository of examples on GitHub or other places where I would go to…
ChrisBartlett
- 93
- 6
9
votes
1 answer
Can a quantum computer tell whether a program is Turing complete?
I am very new to quantum computing and would like to know if a quantum computer can decide whether a given program is Turing complete.
Laith
- 101
- 3
9
votes
2 answers
Allowed CNOT gates for IBM Q 5 quantum computer
I trying to do some tests in the IBM Q5 computer of IBM quantm experience for some simple error correction protocols, but as I can see, some operations between the qubits are not allowed.
For example, it is not possible to perform a CNOT operation…
Josu Etxezarreta Martinez
- 4,136
- 15
- 42
9
votes
3 answers
Magic state distillation: why is it harder to prepare the encoded $|A_{\pi/4}\rangle$ than $|0 \rangle$
My question is the following
Let's assume I am using Steane concatenated code to do error correction. I consider that the stabilizers are extracted fault-tolerantly through the Steane method. The Steane code admits transversal Clifford operations…
Marco Fellous-Asiani
- 2,220
- 2
- 15
- 42
9
votes
1 answer
Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: C29H31N7O?
It is often said that one of the early applications for Quantum Computers will be drug discovery.
Q: Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: $C_{29}H_{31}N_{7}O$ (Imatinib, sold under the brand…
david
- 375
- 1
- 9
9
votes
2 answers
Why do we use ancilla qubits for error syndrome measurements?
Consider the measurement of the syndrome for the standard 3-qubit code to correct bit…
Quantum spaghettification
- 1,532
- 11
- 29
9
votes
2 answers
Minimum number of 2 qubit gates to build any unitary
Any unitary $U$ acting on $N$ qubits can be decomposed in a finite product $U=U_1U_2...U_n$ where every $U_i$ acts on only 2 qubits, for example through decomposition in CNOT, phase shifts and 1 qubit rotations.
Is there a theorem that gives…
Nichola
- 411
- 2
- 9
9
votes
2 answers
How universal is the Toffoli gate for classical reversible computing?
It is easy to see that no finite set of classical reversible gates can be strictly universal (without ancilla) for classical reversible computation: for any reversible gate on $n$ bits, in its action on $n+1$ bits it induces an even permutation, and…
Dylan Thurston
- 263
- 1
- 7
9
votes
2 answers
How does the size of a toric code torus affect its ability to protect qubits?
The Toric code Hamiltonian is:
$\sum_{x,y}\left( \prod_{i\in p(x,y)} Z_{ixy} + \prod_{i\in v(x,y)} X_{ixy} \right),$
where the $v$ and $p$ are defined according to this picture (courtesy of James Wooton's contribution to Wikipedia):
At the moment…
user1271772 No more free time
- 14,286
- 2
- 26
- 76