Construction of an optical quantum computer (OQC) is finished by implementing all necessary ingredients with light (photon). There is, however, one more hurdle to clear. It is scalability, which is easily lost when accommodating many qubits by densel
y nesting quantum circuits. Any of the reported OQC schemes is not neces-sarily best placed in this regard. Here we demonstrate the power of frequency de-gree of freedom of light, which outperforms others with its potentially infinite basis states: as multiple qubits share the same one-photon superposition state all along, a realistic OQC design in frequency basis adopts only one port each for input and out-put. As such quantum logic gates are configurable in a cascade of compact in-line modules, which ensures scalable computing. Finally, our implementation of Deutsch-Jozsas algorithm using standard laboratory laser demonstrates that fre-quency-basis OQC is ideally suited for such tasks even without help of nonclassicality of light.
