R. McDermott, R.W. Simmonds, Matthias Steffen, K.B. Cooper, K. Cicak, K.D.
Osborn, Seongshik Oh, D.P. Pappas, John M. Martinis
Science, 307, pp. 1299-1302 (2005)
One of the many challenges of building a scalable quantum computer is
single-shot measurement of all the quantum bits (qubits). We have used
simultaneous single-shot measurement of coupled Josephson phase qubits to
directly probe interaction of the qubits in the time domain. The concept of
measurement crosstalk is introduced, and we show that its effects are minimized
by careful adjustment of the timing of the measurements. We observe the
antiphase oscillation of the two-qubit |01> and |10> states, consistent
with quantum mechanical entanglement of these states, thereby opening the
possibility for full characterization of multiqubit gates and elementary
quantum algorithms.