# What is a trace in quantum mechanics?

In quantum mechanics, a trace is a measure of the degree of quantum coherence between two states. It is a measure of the extent to which the two states are “entangled” or “correlated” with each other. The trace of a quantum state is a complex number that can be used to calculate the expectation value of any observable quantity in that state. The trace of a quantum state is also a measure of the amount of information that can be extracted from that state.

## Other related questions:

### Q: What is a partial trace in physics?

A: In physics, the partial trace is a way of taking the trace of a matrix that is not square. The partial trace is a special case of the more general concept of a Schur complement.

### Q: How is trace operator calculated?

A: The trace operator is a linear operator that maps a square matrix to a scalar value. The trace of a matrix is the sum of the diagonal elements of the matrix.

### Q: Is Cptp partial trace?

A: Yes, the CPTTP is a partial trace.

### Q: What is measure in quantum computing?

A: In quantum computing, a measure is a unitary operator that is applied to a quantum state in order to obtain information about that state. The measure operator is usually represented by a matrix, and the result of the measure is a set of eigenvalues that correspond to the eigenvectors of the matrix.