Quantum computing with cold atoms and Rydberg blockade

Krittika Goyal, Ivan Deutsch

Andrew Schwarzkopf, David Alexander Anderson, Georg A. Raithel

When cold atoms are laser-excited to Rydberg states, the strong interactions between Rydberg excitations can lead to complex many-body entanglement in the system. The excitation process results in spatial correlations between excitations in the system. In most cases, Rydberg excitation positions are anticorrelated such that no two excitations are within a "blockade radius" of each other. Such systems are well-suited for studying basic many-body physics, as well as for future technological applications such as quantum computation. This thesis describes an experimental apparatus we constructed to perform spatially-sensitive detection of Rydberg atoms. We use the apparatus to perform measurements of the Rydberg-Rydberg pair-correlation function. This results in the first direct spatial images of the Rydberg blockade effect. We measure the blockade radius for a variety of S and D Rydberg states in rubidium. We investigate the dependence of the blockade radius on laser detunings and energy level shifts induced by optical potentials due to trapping lasers. Our results have some implications for atom traps used for neutral atom quantum computation. We also present simulations results used to characterize the performance of the imaging system.

Tyler Keating, Krittika Goyal, Ivan Deutsch

Mark E. Saffman

Mark E. Saffman, T. Xia, Martin Lichtman +2 more

We are exploring several different approaches towards scalable quantum computing based on neutral atom qubits with long range Rydberg blockade. Rydberg interactions can be used to entangle single atom qubits, to entangle ensemble qubits, and to establish hybrid entanglement between atomic and other qubits. Using a 2D array of atomic qubits we demonstrate high fidelity single qubit control together with entanglement of nearby qubits. The ratio of qubit coherence time to entangling gate time exceeds 1000.

Xin Wang, Tianze Sheng, Sun, Yuan

The cold atom qubit platform emerges as an attractive choice for the next stage of quantum computation research, where a special family of synthetic analytical pulses has considerably improved the experimental performance of Controlled-PHASE Rydberg blockade gates in recent studies. The success of Controlled-PHASE Rydberg blockade gates triggers the intriguing question of whether the two-qubit Rydberg blockade gate SWAP gate exists. Via investigating the transition linkage structure, we provide a definitive answer to this question and establish the method of fast SWAP Rydberg blockade gates with synthetic continuously-modulated driving. These gate protocols use careful analysis to properly generate coherent population transfer and phase accumulation of the wave function in the atom-laser interaction process. They can adapt to finite Rydberg blockade strengths and bear considerable resistance some major adverse effects such as laser fluctuations. Further examinations reveal that we can anticipate satisfying performances of the method with currently available experimental techniques in relevant research areas.