Let we have two qubits A and B. First qubit has eigenstates |A0> and |A1>, and second has |B0> and |B1>.(adsbygoogle = window.adsbygoogle || []).push({});

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 matrix, describing only first qubit separately? Is this matrix 1x1 or 2x2?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# What is density matrix of one on two entangled qubits?

**Physics Forums | Science Articles, Homework Help, Discussion**