Also known as Rydberg · tweezer arrays · Rydberg blockade · neutral atom quantum computing
Neutral-atom arrays hold single atoms in optical tweezers and make them interact by exciting them to Rydberg
states, whose strong dipole–dipole interaction blocks double excitation within a few micrometres
[1, 2]. Arrays of hundreds of atoms in arbitrary geometries serve both as analog
quantum simulators and as gate-based processors [3]. The atoms are identical and the qubits
long-lived. The controls are lasers, often applied globally, and tweezers that can rearrange and move the atoms.
Building the array
Tweezers are loaded randomly. Imaging and moving the atoms one by one then assembles defect-free arrays in one and
two dimensions [4, 5]. Coherent transport of entangled atoms between zones gives
the processor dynamic, non-local connectivity [6].
Gates
Blockade gates. In the blockade regime, only one atom of a pair can be excited, so the laser pulse acquires a
phase that depends on both atoms. A CZ gate can be driven by a global pulse that needs no single-site addressing
[7].
Optimal control. Shaped, analytic DRAG-type pulses reduce leakage and improve Rydberg-gate fidelity
[8]. Numerical and semi-analytic optimal control found the time-optimal CZ and CCZ pulses,
smooth and with only a few parameters [9]. Fast single-pulse gates of this kind, together
with dark states that reduce scattering, gave 99.5% fidelity on up to 60 atoms in parallel
[10]. See Quantum gate synthesis.
Algorithms and logical qubits. Arrays with individually addressed beams have run multi-qubit algorithms
[11]. Logical-level control in a zoned architecture has operated up to 280 physical qubits
[12]. See Control for quantum error correction.
Analog control of many-body states
As simulators, Rydberg arrays implement Ising-type spin models with tunable interactions. Ordered phases were prepared
in a 51-atom array [13], and antiferromagnets in two dimensions with hundreds of atoms
[14], by sweeping the laser detuning. Optimal control prepared GHZ states of up to 20 atoms
[15], following theory proposals for Rydberg lattices [16]. For the maximum-independent-set
problem on up to 289 atoms, variational algorithms were optimized in closed loop on the hardware [17].
See Many-body optimal control, Variational algorithms & QAOA as control and Closed-loop & in-situ optimization.
Programming
Pulse-level software such as Pulser expresses analog and digital sequences for neutral-atom devices
[18]. See Pulse-level compilation.
Limitations
Rydberg states decay and are sensitive to stray electric fields, and laser phase and intensity noise limit gate
fidelity.
Atoms are lost and heated, and both need to be detected and replaced during long computations.
Global control is easy, but local control needs extra beams or light shifts, which bring crosstalk.
Key papers
D. Jaksch, J. I. Cirac, P. Zoller, S. L. Rolston, R. Côté and M. D. LukinFast Quantum Gates for Neutral AtomsPhys. Rev. Lett.85, 2208-2211 (2000)doi
Proposes fast neutral-atom gates using strong dipole–dipole interactions between Rydberg states — the blockade mechanism.
M. Saffman, T. G. Walker and K. MølmerQuantum information with Rydberg atomsRev. Mod. Phys.82, 2313-2363 (2010)doi
Review of quantum information with Rydberg atoms.
Antoine Browaeys and Thierry LahayeMany-body physics with individually controlled Rydberg atomsNat. Phys.16, 132-142 (2020)doi
Review of many-body physics with individually controlled Rydberg atoms in tweezer arrays.
Sven Jandura and Guido PupilloTime-Optimal Two- and Three-Qubit Gates for Rydberg AtomsQuantum6, 712 (2022)doi
Time-optimal CZ and CCZ pulses for Rydberg atoms, found with optimal control.
Simon J. Evered, Dolev Bluvstein, Marcin Kalinowski, Sepehr Ebadi, Tom Manovitz, et al.High-fidelity parallel entangling gates on a neutral-atom quantum computerNature622, 268-272 (2023)doi
99.5% two-qubit gates on up to 60 atoms in parallel, using single-pulse gates based on optimal control.
A. Omran, H. Levine, A. Keesling, G. Semeghini, T. T. Wang, et al.Generation and manipulation of Schrödinger cat states in Rydberg atom arraysScience365, 570-574 (2019)doi
GHZ states of up to 20 atoms prepared with optimal control of the many-body system.
Software
Pulser — pulse sequences for neutral-atom arrays, digital and analog, with emulation
References
D. Jaksch, J. I. Cirac, P. Zoller, S. L. Rolston, R. Côté and M. D. LukinFast Quantum Gates for Neutral AtomsPhys. Rev. Lett.85, 2208-2211 (2000)doi
M. Saffman, T. G. Walker and K. MølmerQuantum information with Rydberg atomsRev. Mod. Phys.82, 2313-2363 (2010)doi
Antoine Browaeys and Thierry LahayeMany-body physics with individually controlled Rydberg atomsNat. Phys.16, 132-142 (2020)doi
Manuel Endres, Hannes Bernien, Alexander Keesling, Harry Levine, Eric R. Anschuetz, et al.Atom-by-atom assembly of defect-free one-dimensional cold atom arraysScience354, 1024-1027 (2016)doi
Daniel Barredo, Sylvain de Léséleuc, Vincent Lienhard, Thierry Lahaye and Antoine BrowaeysAn atom-by-atom assembler of defect-free arbitrary two-dimensional atomic arraysScience354, 1021-1023 (2016)doi
Dolev Bluvstein, Harry Levine, Giulia Semeghini, Tout T. Wang, Sepehr Ebadi, et al.A quantum processor based on coherent transport of entangled atom arraysNature604, 451-456 (2022)doi
Harry Levine, Alexander Keesling, Giulia Semeghini, Ahmed Omran, Tout T. Wang, et al.Parallel Implementation of High-Fidelity Multiqubit Gates with Neutral AtomsPhys. Rev. Lett.123, 170503 (2019)doi
L. S. Theis, F. Motzoi, F. K. Wilhelm and M. SaffmanHigh-fidelity Rydberg-blockade entangling gate using shaped, analytic pulsesPhys. Rev. A94, 032306 (2016)doi
Sven Jandura and Guido PupilloTime-Optimal Two- and Three-Qubit Gates for Rydberg AtomsQuantum6, 712 (2022)doi
Simon J. Evered, Dolev Bluvstein, Marcin Kalinowski, Sepehr Ebadi, Tom Manovitz, et al.High-fidelity parallel entangling gates on a neutral-atom quantum computerNature622, 268-272 (2023)doi
T. M. Graham, Y. Song, J. Scott, C. Poole, L. Phuttitarn, et al.Multi-qubit entanglement and algorithms on a neutral-atom quantum computerNature604, 457-462 (2022)doi
Dolev Bluvstein, Simon J. Evered, Alexandra A. Geim, Sophie H. Li, Hengyun Zhou, et al.Logical quantum processor based on reconfigurable atom arraysNature626, 58-65 (2024)doi
Hannes Bernien, Sylvain Schwartz, Alexander Keesling, Harry Levine, Ahmed Omran, et al.Probing many-body dynamics on a 51-atom quantum simulatorNature551, 579-584 (2017)doi
Pascal Scholl, Michael Schuler, Hannah J. Williams, Alexander A. Eberharter, Daniel Barredo, et al.Quantum simulation of 2D antiferromagnets with hundreds of Rydberg atomsNature595, 233-238 (2021)doi
A. Omran, H. Levine, A. Keesling, G. Semeghini, T. T. Wang, et al.Generation and manipulation of Schrödinger cat states in Rydberg atom arraysScience365, 570-574 (2019)doi
Jian Cui, Rick van Bijnen, Thomas Pohl, Simone Montangero and Tommaso CalarcoOptimal control of Rydberg lattice gasesQuantum Sci. Technol.2, 035006 (2017)doi
S. Ebadi, A. Keesling, M. Cain, T. T. Wang, H. Levine, et al.Quantum optimization of maximum independent set using Rydberg atom arraysScience376, 1209-1215 (2022)doi
Henrique Silvério, Sebastián Grijalva, Constantin Dalyac, Lucas Leclerc, Peter J. Karalekas, et al.Pulser: An open-source package for the design of pulse sequences in programmable neutral-atom arraysQuantum6, 629 (2022)doi
Recent papers
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Fault tolerant quantum computers greatly benefit from having both high fidelity entangling gates and a non-local qubit connectivity. However, most entangling gates for neutral atoms are local, requiring separated atoms to be moved using optical tweezers to yield entanglement between them. Here, we design a high fidelity Mølmer Sørensen-like entangling gate between neutral atoms coupled to a photonic cavity, enabling a programmable all-to-all connectivity through the shared cavity coupling. The gate is both robust to changes in cavity photon number, and enables selective entanglement between any subset of separated atoms through local laser addressing. This eliminates the need to physically move atoms to perform the gate, and therefore motional errors and erasure are suppressed. Using experimentally realistic parameters we demonstrate gate fidelities exceeding $F > 0.99$, with higher fidelities achievable through optimal control of the pump amplitudes.
Learning the Hamiltonian of a many-body system from its dynamics is a central task in quantum science, yet the algorithms with the strongest provable guarantees assume some level of quantum control--fast, arbitrary single-qubit gates interleaved with time evolution, and measurements in arbitrary bases--that is beyond the capabilities of near-term analog quantum simulators. Motivated by analog atom- and ion-based platforms, we study Hamiltonian learning under minimal access models. Uniform state preparation and measurements: We first consider the setting where in every experiment, one can rotate each qubit to the same state, perform short-time evolution, and measure every qubit in the same basis. Surprisingly, we show that for generic 2-local Hamiltonians on any interaction graph, all of the parameters can be reconstructed from such experiments. Computational basis state preparation and measurements: We then consider a similarly constrained setting, but where state preparation and measurement are restricted to the computational basis. For nearest-neighbor Hamiltonians with only Pauli $X/Z$ interactions, a class which captures contemporary Rydberg atom platforms, we show that over 1D and 2D rectangular lattices, all of the parameters can be reconstructed from such experiments up to unavoidable gauges. Our protocols introduce new techniques for solving structured polynomial systems over an extensive number of parameters. Taken together, our results suggest that one can learn a great deal from the dynamics of quantum many-body systems even under the most stringent experimental constraints.
Scalable quantum processors require repeated qubit initialization throughout large arrays. In semiconductor spin qubits, fast initialization commonly relies on local reservoir access or measurement-based feedback, requiring dedicated infrastructure that becomes increasingly difficult to distribute as processors scale. Here, we demonstrate reservoir- and measurement-free initialization of a silicon spin-qubit pair in an industrially fabricated Si/SiGe quantum-dot device using a fixed sequence of microwave and baseband pulses. Odd spin-parity states relax to the singlet charge state, whereas blocked even spin-parity states are microwave-driven through the triplet manifold and subsequently converted to the singlet by singlet-triplet mixing and charge hybridization. Repeated cycles produce the singlet-associated charge outcome with a median probability of 99.4% across the sampled preparation states, while exchange spectroscopy independently verifies mapping to the target $|\uparrow\downarrow\rangle$ operational state. Microwave spectroscopy and time-domain measurements identify the dark-state-limited single-cycle transfer and the subsequent blockade-lifting dynamics that set the initialization time scale. The demonstrated pumping sequence uses approximately $12\,μ\mathrm{s}$ of microwave bursts and mixing dwells, while we project sub-microsecond initialization under improved device conditions. These results establish fixed-sequence microwave initialization as a scalable control primitive for semiconductor spin-qubit processors, based on singlet-triplet physics that can be adapted to platforms with suitable Pauli-blockade transitions.
Efficient end-to-end entanglement distribution in quantum information networks requires routing under limited resources and fidelity constraints. We study entanglement routing as a fidelity-constrained unsplittable multicommodity flow problem that maximizes the number of admitted requests. As a proof of concept, we integrate neutral-atom quantum optimization into a hybrid classical--quantum column-generation framework. A classical restricted master problem selects routes, while a pricing problem generates fidelity-feasible paths. We formulate this NP-hard constrained shortest-path pricing problem as a quadratic unconstrained binary optimization (QUBO) problem and address it with hardware-aware register embedding and instance-driven pulse shaping. To our knowledge, this is the first study of neutral-atom quantum optimization as a pricing oracle for fidelity-constrained entanglement routing. On small benchmark instances evaluated with neutral-atom processor emulators, the method, combined with warm-start and post-processing, achieves an optimality gap below 1% across all tested sizes; the selected simulated-annealing route-generation baseline exhibits gaps of up to 6%. These results indicate that the generated bitstrings can provide useful candidate routes for classical refinement within column generation. This proof of concept does not establish quantum utility or scalability; further evaluation on larger instances, against stronger classical baselines, and on quantum hardware is needed.
Arrays of neutral atoms excited to Rydberg levels have emerged as one of the most promising platforms for quantum computation and simulation. With the hope to outperform classical devices, the number of atoms has been increased by orders of magnitude. However, the interaction time, i.e., the maximum accumulated time during which an atom interacts with its neighbours, has been limited to a few microseconds only. This restrains the number of gates per atom or prevents the simulation of long-time dynamics of quantum many-body systems. Here, we observe the spin-exchange interaction between two spin 1/2s encoded in laser-trapped circular Rydberg atoms over more than $60μs$ and 40 spin-oscillation periods, improving the state of the art by an order of magnitude. These unprecedented timescales allow us to record for weak atomic trapping a collapse and revival of the spin-exchange oscillation contrast induced by spin-motion coupling. Our results constitute the first observation of this coupling with laser-trapped Rydberg atoms. To counteract its detrimental effect for quantum simulation, we demonstrate a novel dynamical decoupling method that prevents the collapse of the spin oscillations. This method exploits the advantages of our recently developed hybrid platform that enables the measurement and the optical manipulation of long-lived circular Rydberg atoms with auxiliary Rydberg atoms. This work opens a direct route to long-duration quantum simulation of strongly-interacting many-body systems.