Here we introduce some potential quantum computation candidates instead of superconducting qubits. In comparison, we focus on the following essential features of quantum computation.
Linear Optical quantum computation (LOQC)1, based on the multi-freedom and high robustness of photons is one candidate of future quantum computers beyond solid-state systems. Moreover, as photon travels as the speed of light in space approximately, it is also an outstanding medium to carry information, such as the schema of quantum teleportation and quantum key distribution.
Trapped Ion is another kind of solid-state system for QC2, that is to say, convenient to integrated in a whole chip like superconducting qubit system. First is trapping the ions in separated quantum wells by using Coulomb force. After manipulation by laser, to realize quantum entanglement, we can detune the Coulomb interaction between two neighboring quantum wells.
NMR system has the intrinsic two-level system, the electron spin. Like other systems, RF pulses and delay times is to realize the quantum gates. The most useful advantage of NMR is that it is easy to achieve coherence time around several seconds. To make solid-state NMR devices, people usually turn to electron spin qubits.
Cavity QED is the study of the interaction between the light confined in a reflective cavity and atoms or other particles3. Usually, the atoms are in two-level energy systems and interact with the optical modes of the cavity, a basic entanglement state, so-called Bell states, is composed of both the atomic energy level and the cavity mode. Of course, to change the atomic energy system, people will change the oscillation situation between the cavity-atomic systems.
Topological Computation is some of the new architecture, which is quite different from the above candidates and still in discussion. As we know from quantum mechanics, the symmetry and principle of identity require that exchanging the particles merely brings the phase difference. As a result, the particles, neither fermionic nor bosonic, are named in non-Abelian particles45. By using non-Abelian particles[], it can achieve both the high robustness and easy manipulation at the same time.
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Non-Abelian Discrete Symmetries in Particle Physics. arXiv:1003.3552 [hep-th], doi: 10.1143/PTPS.183.1 ↩