Questions tagged [measurement]

For questions related to measurement and its effects as relevant to quantum computation and quantum information.

106 questions
Filter by
Sorted by
Tagged with
19 views

What's the difference between observing in a given direction and operating in that same direction?

So starting with an up particle: $$\lvert \uparrow \rangle = \begin{bmatrix} 1 \\ 0 \\ \end{bmatrix}$$ My understanding is that you can measure $\lvert \uparrow \rangle$ in $X$ and have ...
16 views

Is manual or automated error correction more practically promising in the near term?

I'm curious if there's any consensus on this question among actual practitioners, but please feel free to close it if it's hopelessly opinion-based (since we've only taken baby steps toward the ...
42 views

42 views

48 views

How to show whether two states are indistinguishable or not by measuring in a different basis?

I'm struggling with understanding a bit of basic quantum mechanics math that I was hoping someone could clarify. If I have two states such as these: $$\frac{1}{\sqrt{2}}(|0\rangle+|1\rangle)$$ and ...
39 views

How to decode 2-bit message from 2 entangled qubits?

I'm trying to do exercise 3 of this quantum course. Alice and Bob prepare an EPR pair in the Bell + state. They each take one qubit home. Suddenly, Alice decides she wishes to convey one of 4 ...
215 views

Does the Copenhagen interpretation (+ “quasi-classical measuring apparatus”) allow one to bypass a derivation's objection?

Background I previously asked this question, in which I'm trying to better understand this joshphysics's derivation of an interpretation of the time-energy uncertainty principle. And the gist of ...
54 views

Help in understanding an exercise on observable / measurement

I'm working through Quantum Computing for Computer Scientists (Yanofsky & Mannucci, 2008), and am getting a little confused about Observables. From what I understand an observable is a question ...
30 views

What is the state after entangled qubit transfer?

Suppose Alice has 2 qubit entangled state and wants to send 1st qubit to Bob. q1) Now what is left with Alice? Both 1st and 2nd qubits or only 2nd qubit? q2) Does the overall composite quantum ...
49 views

Is measuring real qubit states in a complex basis such as $|0\rangle\pm i|1\rangle$ possible?

Say I want to measure a photon in state $\dfrac{\sqrt 2}{2}|0\rangle-\dfrac{\sqrt 2}{2}|1\rangle$ in the measurement basis $[|i\rangle,|-i\rangle]$.
69 views

In the CHSH inequality, how can I know which term is supposed to have the minus sign?

I try to follow the calculation from IBMQ experience regrading of Entanglement and Bell test which they derive the value of question as \begin{equation} C=\langle A B\rangle-\left\langle A B^{\prime}\...
57 views

252 views

How to calculate an Expected Value of some operator acting on qubits?

I'm trying to implement the Variational Quantum Eigensolver in Qiskit. Suppose, I have an operator $A = \sigma_1^z\sigma_2^z$ acting on some two-qubit state $|\psi\rangle$. After a measurement I get ...
92 views

Measurements in Qiskit

What is the difference between 2 types of measurements depicted below? At the end of unitary evolution, qubits are in superposition of states, and after measurement I get a set of probabilites ...
56 views

What's the probability of measuring outcomes give measurement observable $M$ and state $\rho$ when $\mathrm{Tr}\!\:(\!\!\;M\rho)$ is a complex value?

I'm studying the measurement in quantum computation. It's known that the trace is related to the expectation value and the probability of getting certain outcomes. However, when the trace is a complex ...