# All Questions

922 questions
16 views

After installing qiskit-terra via git (pip install qiskit), all python programs involving the line ...
10 views

### Solution enumeration algorithm?

Suppose I have a quantum algorithm that produces, as solutions more than one different linear combinations with raised probability amplitudes. Each solution is correct in the context of this ...
12 views

### What does teleportation have to do w/ XOR linked lists?

I am trying to wrap my head around the correlation between repeating teleportation & XOR linked lists. I understand that: "the quantum equivalent of the one time pad (i.e. XORing a message with ...
22 views

### Clock matrix vs matrix clock

In the process of research leading up to my previous question, I found out about matrix, vector & logical clocks. The citation in the aforementioned question mentions clock and shift matrices. ...
19 views

### Generalizing quantum teleportation for qudits

In an answer to a previous question, Generalization for n quantum teleportations, Craig Gidney states: The more complicated way to generalize teleportation is figuring out how to make it work on ...
30 views

### Multiple random coin flips without measurements

The question is similar to this one. As suggested in the answer, I can easily do this with just one qubit: I repeatedly Hadamard it and measure in order to have a fair coin flip at every point. The ...
26 views

### Partial Trace over a complicated looking state

In the Quantum Operations section in Nielsen and Chuang, (page 358 in the 2002 edition), they have the following equation: $$\varepsilon(\rho) = tr_{env} [U(\rho \otimes \rho_{env})U^\dagger]$$ They ...
59 views

### Depolarizing channel operator sum representation

In Nielsen and Chuang, it is shown that the operator sum representation of a depolarizing channel $\mathcal{E}(\rho) = \frac{pI}{2} + (1-p)\rho$ is easily seen by substituting the identity matrix with ...
92 views

### Are there emulators for quantum networks?

Inspired by the question Are there emulators for quantum computers?, I'm curious to know if it's possible to emulate a quantum network on a classic computer. Additionally, is it possible to emulate a ...
51 views

### Shannon entropy is least when Measurement basis = Mixture basis

For a one qubit system, take a basis. Call this the mixture basis. Consider only basis states and classical mixtures of these basis states. Definition of Shannon Entropy used here: Defined with ...
45 views

35 views

### How many Kraus operators are required to characterise a channel with different start and end dimensions?

If we have a quantum channel mapping from a $d$-dimensional state to a $d$-dimensional state, it can be described by at most $d^2$ Kraus operators. Suppose our channel maps instead from a $d_1$-...
69 views

### How to get all combinations of given input?

I'm stuck with a very specific problem that I'm not sure on how to implement using quantum gates. Suppose I have an n qubit circuit and that I want in output a ...
41 views

### Measuring order ancilla qubits in surface code

Recently I have been reading about surface codes a little and one thing I came acros was a specific order in which gates should be applied before the ancilla is measured. See for instance figure 2 in ...
42 views

### Why are these circuits not producing the same output?

I am simulating the phase shift algorithm on the Quirk platform. Even when the endian-ness of the built-in inverse QFT gate is corrected for, the circuits still output different results. Shouldn't the ...
90 views

### Quantum algorithms for problems outside NP

What is known about quatum algorithms for problems outside NP (eg NEXP-complete problems), both theoretically like upper & lower speedup bounds and various (im)possibility results, as well as ...
46 views

### Implementation of inverse QFT?

When implementing the inverse quantum Fourier transform, in addition to reversing the circuit, does one need to take the conjugate transpose of the phase shift gates in the circuit as well?
31 views

### How are nonlocal games used in device-independent quantum cryptography?

As I understand it, device-independent quantum cryptography enables you to safely perform cryptographic operations without necessarily trusting the quantum device on which they are performed. Nonlocal ...
38 views

### Why are these circuits not producing the expected output?

This circuit was created on the Quirk platform. I'm trying to implement a basic case of phase estimation. For some reason, I'm getting this strange result. When the Inverse QFT is broken down, it ...
85 views

### Non-layperson explanation of why a qubit is more useful than a bit?

I have a computer science and mathematics degree and am trying to wrap my head around quantum computing and it just doesn't seem to make sense from the very beginning. I think the problem is the ...
61 views

### A question about notation for quantum states

I am reading an article on representation of digital images using qubits. But I am not able to understand the notations of the article. Can somebody help me: $|0\rangle$: It means the first basis ...
28 views

### Are the order finding and period finding algorithms the same thing?

Do they both just use similar methods of calculation, or are they completely interchangeable?
30 views

### Do these outputs seem normal for the order finding algorithm?

I'm sorry for posting so many questions about this specific problem, but I just want to make sure that I am implementing an algorithm correctly. I am simulating the order finding algorithm (finding ...
31 views

31 views

### What's the notion of input size for Quantum Verification?

I've been looking into $\mathsf{QPIP}_\tau$ as a complexity class. The following will be a summary of definition 3.12 in Classical Verification of Quantum Computations by Urmila Mahadev. A language ...