Study of Decoherence in Quantum Computers: A Circuit-Design Perspective

Decoherence of quantum states is a major hurdle towards scalable and reliable quantum computing. Lower decoherence (i.e., higher fidelity) can alleviate the error correction overhead and obviate the need for energy-intensive noise reduction techniques e.g., cryogenic cooling. In this paper, we performed a noise-induced decoherence analysis of single and multi-qubit quantum gates using physics-based simulations. The analysis indicates that (i) decoherence depends on the input state and the gate type. Larger number of $|1\rangle$ states worsen the decoherence; (ii) amplitude damping is more detrimental than phase damping; (iii) shorter depth implementation of a quantum function can achieve lower decoherence. Simulations indicate 20\% improvement in the fidelity of a quantum adder when realized using lower depth topology. The insights developed in this paper can be exploited by the circuit designer to choose the right gates and logic implementation to optimize the system-level fidelity.