Final answer:
Quantum gates are guaranteed to be unitary due to the mathematical principles of quantum physics. Photonic quantum gates achieve unitarity through careful design and manipulation of photon properties.
Step-by-step explanation:
A quantum gate is guaranteed to be unitary due to the mathematical principles of quantum physics. In quantum mechanics, a unitary transformation is a linear operator that preserves the inner product of vectors, which means it does not change the normalization or the angles between vectors. When a quantum gate is implemented, it must satisfy this requirement in order to ensure the conservation of probability and the preservation of quantum information. For photonic quantum gates specifically, unitarity is achieved through careful design and manipulation of the properties of photons. Photons can be used as quantum bits, or qubits, in quantum computation. By using techniques such as beam splitters, waveplates, and phase shifters, photonic quantum gates can be constructed to perform specific quantum operations that are unitary in nature. It is important to note that while unitarity is a fundamental requirement for quantum gates, the physical implementation and realization of unitary transformations in various systems can differ based on the specific technology or platform being used.