# Tag Info

Accepted

### Why are only projective measurements considered in nonlocal games to get optimal strategy?

As you correctly state, POVMs can be dilated into a projective measurement on a larger Hilbert space. Because we do not restrict the possible dimension of the Hilbert spaces in the game, we can ...
• 5,958

### Definition of a quantum gate

Sometimes people mean unitary-only. Sometimes they mean generically anything you might do to the qubits (like a measurement gate or a reset gate or a dynamical decoupling gate or a leakage removal ...
• 38.5k

### How to mathematically describe the action of CNOT on the control qubit alone?

The action $\mathcal{E}$ of CNOT on just the control qubit is the composition of two functions: the action \begin{align} \mathcal{C}(\rho)=\text{CNOT}\,\rho\,\text{CNOT}\tag1 \end{align} of CNOT on ...
• 23k
Accepted

### Measuring stabilizers for qutrit stabilizer code

$\def\braket#1#2{\langle#1|#2\rangle}\def\bra#1{\langle#1|}\def\ket#1{|#1\rangle}$ I think your confusion lies with measuring qudit Pauli operators. It is true that operators like $X$ and $Z$ are not ...
• 118
Accepted

### Can Bell states be reexpressed with respect to arbitrary local bases?

A maximally entangled state like $|00\rangle+|11\rangle$ can be generally written as $$\frac{|00\rangle+|11\rangle}{\sqrt2} = |u_0, \bar u_0\rangle+|u_1,\bar u_1\rangle$$ for any pair of orthonormal ...
• 25.5k

### Definition of a quantum gate

I wouldn't say it's coupled with the measurement gate. I think they are inherently different: A quantum gate is equivalent to a Unitary matrix. Quantum gates create together a quantum circuit (which, ...
Accepted

### Why do Surface codes generate so much measurement data?

In a surface code, half the qubits are measurement qubits used to measure the stabilizers. In a superconducting chip you can run a surface code cycle, measuring all the stabilizers, in less than a ...
• 38.5k
Accepted

### Conditioned measurement on bell basis states

Since you don't give your calculations, it's a bit hard to say where you're going wrong! If I do the calculations, I get \begin{align*} \langle pp|M_0|pp\rangle&=2p(1-p) \\ \langle pp|M_3|pp\...
• 59.3k