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Register a new userEntanglement of Two Atoms using Rydberg Blockade
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Over the past few years we have built an apparatus to demonstrate the entanglement of neutral Rb atoms at optically resolvable distances using the strong interactions between Rydberg atoms. Here we review the basic physics involved in this process: loading of single atoms into individual traps, state initialization, state readout, single atom rotations, blockade-mediated manipulation of Rydberg atoms, and demonstration of entanglement.
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We demonstrate the first deterministic entanglement of two individually addressed neutral atoms using a Rydberg blockade mediated controlled-NOT gate. Parity oscillation measurements reveal an entanglement fidelity of $F=0.58pm0.04$, which is above the entanglement threshold of $F=0.5$, without any correction for atom loss, and $F=0.71pm0.05$ after correcting for background collisional losses. The fidelity results are shown to be in good agreement with a detailed error model.
We demonstrate experimentally that a single Rb atom excited to the $79d_{5/2}$ level blocks the subsequent excitation of a second atom located more than $10 murm m$ away. The observed probability of double excitation of $sim 30%$ is consistent with a theoretical model based on calculations of the long range dipole-dipole interaction between atoms.
We use coherent excitation of 3-16 atom ensembles to demonstrate collective Rabi flopping mediated by Rydberg blockade. Using calibrated atom number measurements, we quantitatively confirm the expected $sqrt{N}$ Rabi frequency enhancement to within 4%. The resulting atom number distributions are consistent with essentially perfect blockade. We then use collective Rabi $pi$ pulses to produce ${cal N}=1,2$ atom number Fock states with fidelities of 62% and 48% respectively. The ${cal N}=2$ Fock state shows the collective Rabi frequency enhancement without corruption from atom number fluctuations.
Quantum entanglement is crucial for simulating and understanding exotic physics of strongly correlated many-body systems, such as high--temperature superconductors, or fractional quantum Hall states. The entanglement of non-identical particles exhibits richer physics of strong many-body correlations and offers more opportunities for quantum computation, especially with neutral atoms where in contrast to ions the interparticle interaction is widely tunable by Feshbach resonances. Moreover, the inter-species entanglement forms a basis for the properties of various compound systems, ranging from Bose-Bose mixtures to photosynthetic light-harvesting complexes. So far, the inter-species entanglement has only been obtained for trapped ions. Here we report on the experimental realization of entanglement of two neutral atoms of different isotopes. A ${}^{87}mathrm{Rb}$ atom and a ${}^{85}mathrm{Rb}$ atom are confined in two single--atom optical traps separated by 3.8 $mu$m. Creating a strong Rydberg blockade, we demonstrate a heteronuclear controlled--NOT (C--NOT) quantum gate and generate a heteronuclear entangled state, with raw fidelities $0.73 pm 0.01$ and $0.59 pm 0.03$, respectively. Our work, together with the technologies of single--qubit gate and C--NOT gate developed for identical atoms, can be used for simulating any many--body system with multi-species interactions. It also has applications in quantum computing and quantum metrology, since heteronuclear systems exhibit advantages in low crosstalk and in memory protection.
We show that the use of shaped pulses improves the fidelity of a Rydberg blockade two-qubit entangling gate by several orders of magnitude compared to previous protocols based on square pulses or optimal control pulses. Using analytical Derivative Removal by Adiabatic Gate (DRAG) pulses that reduce excitation of primary leakage states and an analytical method of finding the optimal Rydberg blockade we generate Bell states with a fidelity of $F>0.9999$ in a 300 K environment for a gate time of only $50;{rm ns}$, which is an order of magnitude faster than previous protocols. These results establish the potential of neutral atom qubits with Rydberg blockade gates for scalable quantum computation.
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