Figure 1

(a) Distant spin qubits coupled by an unpolarized spin-chain quantum channel with $g$, the coupling between qubits (yellow, green) and the spin chain, and $\kappa$, the coupling between intrachain elements. Boxed spins, labeled $a^{\prime }$ and $b^{\prime }$, represent additional spin qubits that can correspond to the memory of a quantum register or ancillary qubits associated with quantum information encoding. (b) The spin chain can be reexpressed in terms of free fermions via the Jordan-Wigner transformation, wherein the hopping strength is characterized by $\kappa$. By ensuring that the end spins are resonant with a single fermion mode ($k=z$), unpolarized spin-chain state transfer becomes analogous to fermionic tunneling. Maintaining $g\ll \kappa /\sqrt{N}$ ensures that off-resonant coupling to other fermionic modes can be neglected and enables state transfer independent of the intermediate spin-chain state. (c) Graphlike state generated by FFST between the qubits and the intermediate spin chain [20]. Each line represents a controlled-phase gate.Reuse & Permissions

Figure 2

(a) Numerical simulation of the infidelity of QST for $N=7$ as a function of $g/\kappa$ depicting fluctuations in the infidelity. The upper bound of the numerical infidelity is represented by the bold line. (b) For a chosen tolerable infidelity ${ϵ}_0={10}^{-3}$, the minimum time $\tau$ (in units of $1/\kappa$) required for state transfer scales linearly with chain length.Reuse & Permissions