Abstract
In this paper we propose a Rydberg entangling gate scheme which we demonstrate theoretically to have an order-of-magnitude improvement in fidelities and speed over existing cold atom protocols. It requires a large Rabi frequency compared to the interaction strength, which is difficult in cold atoms, but natural in donors in silicon, where it could help overcome the strenuous requirements on atomic precision donor placement and substantial gate tuning, which so far has hampered scaling. Furthermore, the gate operation would be ultrafast, on the order of picoseconds. We calculate multivalley van der Waals, induced electric dipole and total Rydberg interactions for several donor species using the finite-element method and show that they are important even for low-lying excited states. We show that Rydberg gate operation is possible within the lifetime of donor excited states with 99.9% fidelity for the creation of a Bell state in the presence of decoherence.
Highlights
Donor electron spin qubits in silicon are competitive in most of Di Vincenzo’s criteria for a quantum computer implementation: scalability, high-fidelity initialization and readout, as well as extremely long coherence times [1,2,3,4,5]
Entangling gate schemes in donors so far have focused on harnessing the highly oscillatory and exponentially decaying ground-state ferromagnetic exchange (J) [6,25]: this interaction is negligible in high-lying excited states of Rydberg atoms, where u is dominated by the electric dipole interaction
Iψi(r ), where Ucc is a central-cell potential for the S states, which have a non-negligible probability of being at the core, UE f is the electric field, i is the binding energy of the donor, and m∗ is the effective mass of the electron in the silicon lattice
Summary
Donor electron spin qubits in silicon are competitive in most of Di Vincenzo’s criteria for a quantum computer implementation: scalability (and complementary metal oxide semiconductor, CMOS, compatibility), high-fidelity initialization and readout, as well as extremely long coherence times [1,2,3,4,5]. We show that the theoretical fidelities achievable by our gate protocol are an order of magnitude higher than existing Rydberg atom schemes This is because our gate allows for the excited-state interaction u to be on the same order of magnitude as the Rabi frequency coupling one of the qubit levels |1 spin-selectively (see Fig. 1) to |r. < u, our proposal only requires h/T1 , u, allowing for much smaller gate durations and less probability of decay from |r , leading to higher gate fidelities This is because previous schemes were based on the blockade, in which the doubly excited state |rr is tuned out of resonance due to strong interactions induced by u. We show that these two conditions can be fulfilled in both shallow and deep donors
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