I want to understand the relation between the following two ways of deriving a (unitary) matrix that corresponds to the action of a gate on a single qubit: 1) HERE, in IBM's tutorial, they represent the general unitary matrix acting on a qubit as: $$ U = \begin{pmatrix} \cos(\theta/2) &...

Is there some definition or theorem about what a quantum computer can achieve from which post quantum cryptographic schemes (eg lattice cryptography, but not quantum cryptography) can justify their security? I know the period finding function is capable of breaking RSA and discrete logs, but is i...

What are the P(0) and P(1) probabilities for the T transformation in quantum computing? I commented on DaftWulie's comment. Changing basis brings you from 50:50 to 100:0, so the fact that the experimental measurements gave 85:15 is due to noise. A moderator has come and "trolled" by removing my...

Such a public key cryptosystem would be "quantum safe" in the sense that quantum computers cannot efficiently solve QMA hard problems.

I have been reading about the Quantum Channel Capacity and it seems to be an open problem to find such capacity in general. Quantum capacity is the highest rate at which quantum information can be communicated over many independent uses of a noisy quantum channel from a sender to a receiver. Kno...

I know there are measures that can be taken to mitigate the effects of dephasing (I'm referring here to Dynamic Decoupling and the other ideas it led to). I find it surprising that there is no equivalent procedure to mitigate the effects of energy leakage. In principle, it seems like if you add e...

I don't know much about physics so maybe the question is stupid, but I wonder how engineers detect that the state function did not collapse due to environment while a calculation is performed? Theoretically, a measurement will break the system. Related is also the next question, how to detect tha...

Qudit graph states are $d$-dimension generalisations of qubit graph states such that each state is represented by a weighted graph $G$ (with no self-loops) such that each edge $(i, j)$ is assigned a weight $A_{i, j} = 0,\ldots,d-1$. The graph state associated with $G$ is then given by $$ |G⟩ = \...

I'm looking at this paper and try to implement the Quantum adders they define myself. Suppose we have a number $b=b_{n-1}\dots b_1b_0$ and they want to add a constant number $a=a_{n-1}\dots a_1a_0$. They define $$A_j = \Pi_{k=1}^{j+1} R_k^{a_{j+1-k}}, \quad R_k = \begin{pmatrix}1&0\\0&e^{i2\p...

In C2, we generally take +1 and -1 as the standard eigenvalues, that's what Pauli-x, Pauli-z measurements, etc will give us. Is there a similar standard while measuring in the Bell basis and the computational basis in C2*C2? Of course, the actual eigenvalues don't matter, as long as we are talki...

After taking some measure, how can a qunit be "unmeasured"? Is unmeasurement (ie reverse quantum computing) possible?

I understand opinion based questions are discouraged on the main site. Is it ok to ask them here?

How D-Wave's Pegasus architecture different from the Chimera architecture?