We propose and analyze the implementation of a two-qubit quantum gate using circular Rydberg states with maximum orbital angular momentum. The intrinsic quantum gate error is limited by the finite Rydberg lifetime and finite Rydberg blockade shift. Circular states have much longer radiative lifetimes than low orbital angular momentum states and are therefore candidates for high-fidelity gate operations. We analyze the dipole-dipole interaction of two circular state Rydberg atoms and present numerical simulations of quantum process tomography to find the intrinsic fidelity of a Rydberg blockade-controlled phase gate. Our analysis shows that the intrinsic gate error can be less than $9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ for circular Cs atoms in a cryogenic environment.
We propose and analyze the implementation of a two-qubit quantum gate using circular Rydberg states with maximum orbital angular momentum. The intrinsic quantum gate error is limited by the finite Rydberg lifetime and finite Rydberg blockade shift. Circular states have much longer radiative lifetimes than low orbital angular momentum states and are therefore candidates for high-fidelity gate operations. We analyze the dipole-dipole interaction of two circular state Rydberg atoms and present numerical simulations of quantum process tomography to find the intrinsic fidelity of a Rydberg blockade-controlled phase gate. Our analysis shows that the intrinsic gate error can be less than 9\ifmmode×\else\texttimes\fi10\ensuremath−6 for circular Cs atoms in a cryogenic environment.
We present a detailed error analysis of a Rydberg blockade mediated controlled-not quantum gate between two neutral atoms as demonstrated recently in Isenhower et al. [Phys. Rev. Lett. 104, 010503 (2010)] and Zhang et al. [Phys. Rev. A 82, 030306 (2010)]. Numerical solutions of a master equation for the gate dynamics, including all known sources of technical error, are shown to be in good agreement with experiments. The primary sources of gate error are identified and suggestions given for future improvements. We also present numerical simulations of quantum process tomography to find the intrinsic fidelity, neglecting technical errors, of a Rydberg blockade controlled phase gate. The gate fidelity is characterized using trace overlap and trace distance measures. We show that the trace distance is linearly sensitive to errors arising from the finite Rydberg blockade shift and introduce a modified pulse sequence which corrects the linear errors. Our analysis shows that the intrinsic gate error extracted from simulated quantum process tomography can be under 0.002 for specific states of 87Rb or Cs atoms. The relation between the process fidelity and the gate error probability used in calculations of fault tolerance thresholds is discussed.
Arrays of optically trapped neutral atoms are an emerging platform for scalable quantum computing, where achieving high-fidelity entangling gates remains a central challenge. We present a systematic analysis of the two-qubit controlled-Z (cz) gate under finite Rydberg blockade, paying particular attention to the influence of near-degenerate Rydberg pair states and resonant dipole-dipole interactions. Using the global two-pulse excitation protocol, we model the full gate dynamics, explicitly capturing population leakage into noncomputational states. By analyzing the interplay between the control parameters such as Rabi frequency, detuning, the F\"orster defect, and interaction strength, we identify conditions that enable fast, high-fidelity gate operation while minimizing leakage. We also quantify the impact of finite Rydberg-state lifetimes on gate error and further demonstrate that the optimal parameter regimes identified here are accessible in current rubidium-based tweezer experiments. These results provide practical guidance for optimizing two-qubit gate protocols in neutral-atom quantum processors with experimentally accessible conditions.
Summary form only given. Condensed-matter systems are interesting and important to understand, for fundamental science as well as towards more applied objectives in the development of new materials for instance. Unfortunately, these many-body quantum systems are difficult to study: both the theoretical approach and the numerical simulation are proving impossible to carry out to relevant system sizes. Quantum simulation proposes to mimic those out-of-reach systems with more controllable and accessible quantum systems. Rydberg atoms gained renewed interest in the last decades thanks to their very high polarizability, allowing for strong and tunable short-range interactions. They constitute an interesting candidate for a quantum simulation platform. However, low angular momentum Rydberg states have limited, despite relatively long, lifetimes which limit the scope of such a quantum simulator. Moreover, low-l Rydberg states cannot be efficiently laser-trapped. In order to overcome these limitations, we propose to use circular Rydberg states, i.e., of maximum angular momentum. Circular Rydberg states exhibit much longer lifetimes, and can be trapped using laser light. By placing the circular Rydberg atoms inside a spontaneous emission-inhibiting capacitor, we hope to achieve the deterministic preparation of a 1D-chain of 40 atoms, with a collective lifetime of over 2 seconds. With expected exchange energies in the 10-100 kHz range, this would provide a platform capable of simulating quantum many-body physics up to 105exchange times. The first step towards the experimental realization of such a quantum simulator is the demonstration of the laser-trapping of circular Rydberg atoms. To this end, we use a Laguerre-Gauss hollow beam at 1064 nm, imposing a ponderomotive potential on the nearly-free electron of the Rydberg atoms. I will present our latest experimental results of light-trapping of circular Rydberg atoms.
Stability achieved by large angular momentum is ubiquitous in nature, with examples ranging from classical mechanics, over optics and chemistry, to nuclear physics. In atoms, angular momentum can protect excited electronic orbitals from decay due to selection rules. This manifests spectacularly in highly excited Rydberg states. Low angular momentum Rydberg states are at the heart of recent breakthroughs in quantum computing, simulation and sensing with neutral atoms. For these applications the lifetime of the Rydberg levels sets fundamental limits for gate fidelities, coherence times, or spectroscopic precision. The quest for longer Rydberg state lifetimes has motivated the generation, coherent control and trapping of circular Rydberg atoms, which are characterized by the maximally allowed electron orbital momentum and were key to seminal experiments with single atoms and photons. Here, we report the observation of individually trapped circular Rydberg atoms with lifetimes of more than 10 milliseconds, two orders of magnitude longer-lived than the established low angular momentum orbitals. This is achieved via Purcell suppression of blackbody modes at room temperature. We coherently control individual circular Rydberg levels at so far elusive principal quantum numbers of up to n = 103, and observe tweezer trapping of the Rydberg atoms on the hundred millisecond scale. Our results pave the way for quantum information processing and sensing utilizing the combination of extreme lifetimes and giant Rydberg blockade.
Summary form only given. Quantum simulation offers a highly promising way to understand large correlated quantum systems, and many experimental platforms are now being developed. Rydberg atoms are specially appealing thanks to their strong and short-range dipole-dipole interaction and to their long lifetime. Low-angular momentum Rydberg atoms have been successfully used recently to realize early quantum simulators. These experiments suffer, however, from the limited (despite long) lifetime of these levels and the fact that they cannot be efficiently trapped [1, 2].Here, we propose to use circular Rydberg atoms, i.e., Rydberg atoms with maximum angular momentum, to realize a quantum simulator: A chain of circular atoms is laser trapped inside a spontaneous emission inhibiting structure. A defect-free chain of 40 atoms could be prepared. It is expected to live several seconds inside the inhibition structure. Given the strong interaction frequencies between nearby Rydberg atoms, such a system would, thus, allow us to observe the dynamics of the spin chain over several 10 4 interaction cycles. In addition, the solid state Hamiltonian that would be simulated is fully tuneable experimentally. The proposed circular atoms quantum simulator should therefore open the way towards the simulations of systems and of their dynamics beyond the grasp of classical computation.
Rydberg blockaded gate is a fundamental ingredient for scalable quantum computation with neutral Rydberg atoms. However the fidelity of such a gate is intrinsically limited by a blockade error coming from a Rydberg level shift that forbids its extensive use. Based on a dark-state adiabatic passage, we develop a novel protocol for realizing a two-atom blockade-error-free quantum gate in a hybrid system with simultaneous van der Waals (vdWsI) and resonant dipole-dipole interactions (DDI). The basic idea relies on converting the roles of two interactions, which is, the DDI serves as one time-dependent tunable pulse and the vdWsI acts as a negligible middle level shift, as long as the adiabatic condition is preserved. We adopt an optimized super-Gaussian optical pulse with kπ(k ≫ 1) area accompanied by a smooth tuning for the DDI, composing a circular stimulated Raman adiabatic passage, which can robustly ensure a faster operation time ∼ 80ns as well as a highly-efficient gate fidelity ∼ 0.9996. This theoretical protocol offers a flexible treatment for hybrid interactions in complex Rydberg systems, enabling on-demand design of new types of effective Rydberg quantum gate devices.