Optimal eavesdropping in quantum cryptography. II. A quantum circuit
Robert B. Griffiths, Chi-Sheng Niu · Physical Review A · 1997
It is shown that the optimum strategy of the eavesdropper described in the preceding paper can be expressed in terms of a quantum circuit in a way which makes it obvious why certain parameters take on particular values, and why obtaining information in one basis gives rise to noise in the conjugate basis.