Figure 1
APS/Joan Tycko

Figure 1: How can we tell if a machine is a quantum computer? One way is to prove that the machine can solve problems faster or better than any classical approach. Another test is to look inside the machine and show that its elements (qubits) can form highly entangled states and support quantum superpositions. To claim their device is a quantum computer, Bian et al. [1] would need to show it meets one or both of these challenges.