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An Inside Look at Superconducting Qubits Essay

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Superconducting Qubits

Introduction and Background
The quantum computation has remarkably improved since the use of quan- tum algorithms that have a run time which is exponentially faster compared to classical algorithms. Implementation of theory for practical computation presents various technological and scientific challenges. It is required that the Qubits be entirely free from external noise while at the same time they need to be strongly coupled amongst themselves using gates for computa- tion. We need to construct the qubits such that their degrees of freedom are independent of the noise in the environment. For example electronic spins or spins of nuclei are isolated from surrounding noise. In superconduct- ing qubits …show more content…

These are termed as macroscopic quantum coherence effects.
1.1.2
Superconductivity
On lowering the temperature of some metals (materials) to a scale of few kelvins the electrons experience a net attractive force amongst themselves.
This is attraction is phonon mediated. As a result of bonding between two electrons near the Fermi level the net energy decreases. The pair has a spin zero .The pairing process changes the Fermi level and further formation of pairs takes place which can all occupy the ground state(zero spin state not affected by Paulis exclusion principle).The entire resistance less flow of cooper paired electrons is called as ’supercurrent’. The superconducting state is lower in energy from the normal material state by an amount of energy called the superconducting energy gap. ψ = n0.5 eiθ s Where ns cooper pair density, θ is the superconducting phase.
1.2
Josephson effect
A junction formed by placing two superconducting chips with a thin insula- tor in between is called Josephson junction tunnel. We see that at sufficiently low temperatures such that thermal energy cannot break the cooper pairs, these pairs tunnel from one superconducting electrode to another, even in the absence of biasing voltage.
IJ = Io sin(δ)
1.2. JOSEPHSON EFFECT
3
Where IJ : supercurrent, Io : critical current, h 2e φo =
Where, φo is the quanta of flux. δ = φL − φR

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