Scalable Solid-State Quantum Processor Using Subradiant Two-Atom States

We propose a realization of a scalable, high-performance quantum processor whose qubits are represented by the ground and subradiant states of effective dimers formed by pairs of two-level systems coupled by resonant dipole-dipole interaction. The dimers are implanted in low-temperature solid host material at controllable nanoscale separations. The two-qubit entanglement either relies on the coherent excitation exchange between the dimers or is mediated by external laser fields.

Figure 1

(a) Two TLAs 1 and 2, separated by normalized distance $\zeta$, interact via RDDI and exchange a single excitation. (b) Energy level diagram of the resulting dimer states of the system.

Figure 2

(a) Dimers $A$ and $B$ are separated by normalized distance $\xi >\zeta$. An external ac Stark field can switch on and off the RDDI between the dimers. (b) When the qubit transitions of dimers $A$ and $B$ are brought to resonance, they start swapping a single excitation.

Figure 3

Inset: Schematic drawing of the proposed QP and the geometry for the cphase gate: The interatomic axis of each dimer (SD qubit) is perpendicular to the interdimer axis, ${\mathbf{r}}_{12}^{A,B}\perp {\mathbf{r}}_{AB}$. Each SD qubit can be separately addressed by a laser field with ${\mathbf{k}}_r\parallel {\mathbf{r}}_{12}$. Two-qubit interaction is mediated by a coupling field with ${\mathbf{k}}_c\parallel {\mathbf{r}}_{AB}$. (a) Internal level structure of two dimers. (b) Eigenstates of the combined system of two dimers.