Qubits Definition and 57 Threads

What is the best possible test for differentiating qubits? Assuming we have only ONE copy of each. What if a few (but still small number of) copies were allowed?

A swap-test is described here http://en.wikipedia.org/wiki/Quantum_digital_signature#Public_Key_should_be_the_same_for_every_recipient_.28Swap_Test.29 Now if the target qubits are identical, then after the swap test they are not disturbed. But what happens to them if they weren't identical...

Given two arbitrary qubits, is there a test I can do that will always tell orthogonal qubits apart (but may fail if they are not)? Does it necessarily destroy the qubits' states?

Let we have two qubits A and B. First qubit has eigenstates |A0> and |A1>, and second has |B0> and |B1>. Let them be in the entangled state, described with vector c1 * |A0> * |B0> + c2 * |B0> * |B1>| where c1 and c2 are complex numbers with |c1|^2 + |c2|^2 = 1. Then what is density...

Homework Statement http://img249.imageshack.us/img249/4476/46715318ov5.jpg The Attempt at a Solution I know to calculate the pr we square the number in front of the state. e.g) for state psi 00, the pr is (1/root(2))^2 But for state psi 01, do I include the imaginary number part...

Hello everyone, Could someone explain the basics of the qubit particularly pertaining to quantum computing? Maybe if you know any good links that explain the basics or if you could explain it yourselves. I appreciate it a bunch! Thanks guys!

Anybody read the Scientific American article on them socalled mechanical qubits ? This idea is like this : suppose you have a rope of 10cm long, when you press is together at both ends it will bend towards the right and left side. Now, if you replace this rope by a nanotube of a few...