arXiv subjects

Mohammadsadegh Khazali

Publications and source records attributed to Mohammadsadegh Khazali.

16 recordsLinked to original sources

arXiv2026

Blockade-induced exchange primitives for scalable neutral-atom QPU

Many quantum hardware platforms natively support either phase or exchange operations, yet converting between these two forms of control typically incurs substantial overhead. Rydberg-blockade neutral-atom arrays are highly developed for phase control, while controlled exchange is usually obtained only through depth-intensive decompositions. Here, controlled exchange is realized as a native, blockade-programmed phenomenon in a collective excited manifold. Target atoms are engineered such that two competing exchange pathways between |01> and |10> destructively interfere, while a single collective four-photon channel mediated by a symmetric Rydberg excitation remains resonant and drives a direct SWAP, with all other qubit configurations undergoing an identity action. Exchange conditionality follows from blockade: exciting a control atom to a Rydberg state shifts and blocks the target collective resonance, suppressing exchange, whereas leaving the control in the ground manifold enables exchange in a single step. Anisotropic control-target interactions give rise to selective blockade, enabling coherent programmability of exchange among specific target pairs. This yields a family of controlled-SWAP primitives with process fidelities above 99% and an order-of-magnitude reduction in circuit depth and Rydberg-state exposure time compared with decomposed implementations. The same principle generalizes to multi-control and multiplexed controlled-exchange operations, providing compact hardware-level primitives for conditional information routing in extended neutral-atom arrays. More broadly, engineering interaction-tuned near-degeneracies in collective manifolds offers a route to programmable non-diagonal multiqubit operations across quantum platforms.

quant-ph↗

arXiv2025

Optimal Control for Rydberg multi-qubit operations

Quantum computing algorithms can be decomposed into a universal set of elementary one- and two-qubit gates. Different physical implementations of quantum computing, however, employ interactions that permit direct conditional dynamics on multiple qubits in a single step. In this work, we leverage quantum optimal control techniques to design single continuous laser pulses that implement multi-qubit controlled-phase, -NOT and -swap (Fredkin) gates on Rydberg atom quantum processors. The identification of robust multi-qubit operations leads to reduced operation time and less decoherence, and the control field provides continuous protection of the atoms from environmental noise. Notably, we find that the controlled-swap (Fredkin) gate, implemented using this approach achieves 99.74\% fidelity while accounting for imperfections such as spontaneous emission, laser fluctuations, and Doppler dephasing.

quant-ph↗

arXiv2025

Quasi-Contact Forces with Resonant Range Control in Rydberg Atoms

We introduce a novel method to engineer sharply peaked, distance-selective interactions between neutral atoms by exploiting interaction-induced resonances within a resonantly driven Rydberg ladder system. By tuning laser parameters, a subsystem eigenstate twist rapidly and brought into degeneracy with the atomic ground state at precisely defined interatomic separations, resulting in an effective potential sharply localized around this resonance distance. Unlike previous off-resonant macrodimer-based schemes, our approach significantly enhances interaction sharpness and strength, reaching MHz scales, and provides straightforward experimental tunability without requiring sub-wavelength positional control. Analytic expressions, validated through comprehensive master-equation simulations, detail the interaction profile's amplitude, width, and resonant distance. This precise control facilitates parallel entangling gates crucial for measurement-based quantum computing and enables simulation of complex lattice Hamiltonians with customizable connectivity. Additionally, our scheme opens possibilities for novel studies in molecular physics through micrometer-scale bond-length diatomic molecules.

physics.atom-ph↗

arXiv2025

Quantum computation with longlived Rydberg-Landau atoms featuring suppressed ionization by the Magnetic Cage

Atomic processing units require robust entanglement between individual qubits, typically achieved via excitation to highly interacting Rydberg states. However, short Rydberg lifetimes and ionization risks limit the quantum volume score of the atomic processing units. Inspired by Landau resonances in alkaline atoms, we introduce Rydberg-Landau (rLandau) states created under a strong magnetic field (2.5 Tesla). These states exhibit significantly extended lifetimes and a magnetic confinement mechanism that prevents ionization, even under intense laser fields. We analyze their wavefunctions, excitation dynamics, dipole transition rules, lifetimes, and interactions, identifying states optimal for high-fidelity quantum operations. This approach simplifies the coherent excitation of long-lived, strongly interacting rLandau circular states akin to Coulombic counterparts, enabling deeper and more complex quantum algorithms.

quant-ph↗

arXiv2024

Ultratight confinement of atoms in a Rydberg empowered optical lattice

Optical lattices serve as fundamental building blocks for atomic quantum technology. However, the scale and resolution of these lattices are diffraction-limited to the light wavelength. In conventional lattices, achieving tight confinement of single sites requires high laser intensity, which unfortunately leads to reduced coherence due to increased scattering. This article presents a novel approach for creating an atomic optical lattice with a sub-wavelength spatial structure. The potential is generated by leveraging the nonlinear optical response of three-level Rydberg-dressed atoms, which allows us to overcome the diffraction limit of the driving fields. The resulting lattice comprises a three-dimensional array of ultra-narrow Lorentzian wells over nanometer scales. These unprecedented scales can now be accessed through a hybrid scheme that combines the dipolar interaction and optical twist of atomic eigenstates. The interaction-induced two-body resonance that forms the trapping potential, only occurs at a peculiar laser intensity, localizing the trap sites to ultra-narrow regions over the standing-wave driving field. The feasibility study shows that single-atom confinement in Lorentzian sites with 3nm width, and 37MHz depth are realizable with available lasers. The development of these ultra-narrow trapping techniques holds great promise for applications such as Rydberg-Fermi gates, atomtronics, quantum walks, Hubbard models, and neutral-atom quantum simulation.

quant-ph↗

arXiv2024

Fast multicomponent cat-state generation under resonant or strong-dressing Rydberg-Kerr interaction

Cat states are maximally entangled states with applications in metrology and fault-tolerant quantum computation. The experiments have revealed that Rydberg collective avalanche decoherence acts as the bottleneck for cat creation with Rydberg atoms. This process initiates after the black body radiation (BBR-)induced decay of Rydberg atoms and sets a strong limit on the cat creation time. These findings necessitate the exploration of new ideas to accelerate current Rydberg cat schemes. To enhance the interaction-to-loss ratio, this paper delves into cat state formation in the strong Rydberg dressing regime, uncovering the emergence of cat states despite the presence of complex orders of nonlinearities. This unexplored regime demonstrates the potential for rapid cat state formation, particularly beneficial for operation in typical 2D lattices in Rydberg Labs. In an extreme case, this article demonstrates that second-order nonlinearity could be isolated under resonant Rydberg driving if a large number of atoms are accommodated inside the blockade volume. The resonant model significantly enhances the interaction-to-loss ratio while circumventing the adiabaticity condition, allowing fast switching of lasers. In addition, the paper presents a method for generating multi-component cat states, which are superpositions of $m$ coherent spin states ($|m-\text{CSS}\rangle$). The maximum value of $m$ is determined by the number of atoms within the blockade radius, where $m=\sqrt{N}$. The states with larger $m$ are more robust against the presence of multiple orders of nonlinearity in the strong dressing Hamiltonian and are accessible in a much shorter time compared to traditional 2-component cat states.

quant-ph↗

arXiv2023

All optical quantum information processing via a single step Rydberg blockade gate

One of the critical elements in the realization of the quantum internet are deterministic two-photon gates. This $CZ$ photonic gate also completes a set of universal gates for all-optical quantum information processing. This article discusses an approach to realize high fidelity $CZ$ photonic gate by storing both control and target photons within an atomic ensemble using non-Rydberg electromagnetically induced transparency (EIT) followed by a fast, single-step Rydberg excitation with global lasers. The proposed scheme operates by relative intensity modulation of two lasers used in Rydberg excitation. Circumventing the conventional $π$-gap-$π$ schemes, the proposed operation features continuous laser protection of the Rydberg atoms from the environment noise. The complete spatial overlap of stored photons inside the blockade radius optimizes the optical depth and simplifies the experiment. The coherent operation here is performed in the region that was dissipative in the previous Rydberg EIT schemes. Encountering the main imperfection sources, i.e. the spontaneous emission of the Rydberg and intermediate levels, population rotation errors, Doppler broadening of the transition lines, storage/retrieval efficiency, and atomic thermal motion induced decoherence, this article concludes that with realistic experimental parameters 99.7\% fidelity is achievable.

quant-ph↗

arXiv2023

Electron cloud design for Rydberg multi-qubit gates

This article proposes quantum processing in an optical lattice, using Rydberg electron's Fermi scattering from ground-state atoms in spin-dependent lattices as a source of interaction. Instead of relying on Rydberg pair potentials, the interaction is controlled by engineering the electron cloud of a sole Rydberg atom. Here we specifically propose the implementation of two prominent multi-qubit gates i.e. the stabilizer-phase operator and the Toffoli gate. The new scheme addresses the main bottleneck in Rydberg quantum simulation by suppressing the population of short-lived Rydberg states over multi-qubit operations. This scheme mitigates different competing infidelity criteria, eliminates unwanted cross-talks, and allows operations in dense atomic lattices. The restoring forces in the molecule type Ryd-Fermi potential preserve the trapping over a long interaction period. The features in the new scheme are of special interest for the implementation of quantum optimization and error correction algorithms.

quant-ph↗

arXiv2022

Universal terminal for mobile edge-quantum computing

To bring the quantum computing capacities to the personal edge devices, the optimum approach is to have simple non-error corrected personal devices that offload the computational tasks to scalable quantum computers via edge servers with cryogenic components and fault-tolerant schemes. Hence the network elements deploy different encoding protocols. This article proposes quantum terminals that are compatible with different encoding protocols; paving the way for realizing mobile edge-quantum computing. By accommodating the atomic lattice processor inside a cavity, the entangling mechanism is provided by the Rydberg-Fermi cavity-QED technology. The gate operates by the Fermi scattering of a Rydberg electron from the plaquette atoms hosting the physical qubits. Therefore, different arrangements of logical-qubits derive the central atom over distinguished eigenstates, featuring photon emission at the early or late times distinguished by quantum interference. Applying an entanglement-swapping gate on two emitted photons would make the far-separated qubits entangled regardless of their encoding protocols. This gate provides a universal photonic interface for clustering the processors and connecting them with the quantum memories and quantum cloud that is compatible with different encoding formats.

quant-ph↗

arXiv2022

Discrete-Time Quantum-Walk & Floquet Topological Insulators via Distance-Selective Rydberg-Interaction

This article proposes the first discrete-time implementation of Rydberg quantum walk in multi-dimensional spatial space that could ideally simulate different classes of topological insulators. Using distance-selective exchange-interaction between Rydberg excited atoms in an atomic array with dual lattice-constants, the new setup operates both coined and coin-less models of discrete-time quantum walk (DTQW). Here, complicated coupling tessellations are performed by a global laser that exclusively excites the site at the anti-blockade region. The long-range interaction provides a new feature of designing different topologically ordered periodic boundary conditions. Limiting the Rydberg population to two excitations, coherent QW over hundreds of lattice sites and steps are achievable with the current technology. These features would improve the performance of this quantum machine in running the quantum search algorithm over topologically ordered databases as well as diversifying the range of topological insulators that could be simulated.

quant-ph↗

arXiv2020

Rydberg Noisy-Dressing and applications in making soliton-molecules and droplet quasi-crystals

The current advances in the field of ultra-cold atoms and atomic traps recall new controllable long-range interactions. These interactions are expected to extend the range of realizable quantum algorithms as well as providing new control mechanisms for the new types of quantum matters. This article presents special inter-atomic interactions between Rydberg-dressed atoms by manipulating lasers' line-width. The new interaction features a hybrid spatial profile containing plateaus and Gaussian peaks. Combined with dynamic individual control over the sign and strength of these interaction elements, the Rydberg noisy-dressing (RnD) scheme provides a valuable interaction toolbox for quantum technology. As an example, RnD's application in making stable gigantic 3D soliton molecules and in the formation of quasi-periodic droplet-crystals are discussed.

quant-ph↗

arXiv2020

Fast multi-qubit gates by adiabatic evolution in interacting excited state manifolds

Quantum computing and quantum simulation can be implemented by concatenation of one- and two-qubit gates and interactions. For most physical implementations, however, it may be advantageous to explore state components and interactions that depart from this universal paradigm and offer faster or more robust access to more advanced operations on the system. In this article, we show that adiabatic passage along the dark eigenstate of excitation exchange interactions can be used to implement fast multi-qubit Toffoli (C$_k$-NOT) and fan-out (C-NOT$^k$) gates. This mechanism can be realized by simultaneous excitation of atoms to Rydberg levels, featuring resonant exchange interaction. Our theoretical estimates and numerical simulations show that these multi-qubit Rydberg gates are possible with errors below 1% for up to 20 qubits. The excitation exchange mechanism is ubiquitous across experimental platforms and we show that similar multi-qubit gates can be implemented in superconducting circuits.

quant-ph↗

arXiv2018

Towards macroscopic spin and mechanical superposition via Rydberg interaction

This paper is a proposal for the generation of many-body entangled state in atomic and mechanical systems. Application of strong Rydberg dressing interaction and fast bifurcation scheme in an ultra-stable Cs lattice clock in this proposal results to a breakthrough in the formation of large cat states. By detailed study of the de-coherence effects using Quantum Jump Monte Carlo approach and considering obstacles in dense ensembles namely level mixing, molecule formation and collective decoherence this proposal predicts the formation of 700 atoms cat state. Dipole coupling between Rydberg atoms and charged cantilevers is proposed for the transfer of the generated superposition to far separated mechanical oscillators.

quant-ph↗

arXiv2017

Single-photon source based on Rydberg exciton blockade

We propose to implement a new kind of solid-state single-photon source based on the recently observed Rydberg blockade effect for excitons in cuprous oxide. The strong interaction between excitons in levels with high principal quantum numbers prevents the creation of more than one exciton in a small crystal. The resulting effective two-level system is a good single-photon source. Our quantitative estimates suggest that GHz rates and values of the second-order correlation function $g_2(0)$ below the percent level should be simultaneously achievable.

quant-ph↗

arXiv2016

Large Energy Superpositions via Rydberg Dressing

We propose to create superposition states of over 100 Strontium atoms being in a ground state or metastable optical clock state, using the Kerr-type interaction due to Rydberg state dressing in an optical lattice. The two components of the superposition can differ by of order 300 eV in energy, allowing tests of energy decoherence models with greatly improved sensitivity. We take into account the effects of higher-order nonlinearities, spatial inhomogeneity of the interaction, decay from the Rydberg state, collective many-body decoherence, atomic motion, molecular formation and diminishing Rydberg level separation for increasing principal number.

quant-ph↗

arXiv2014

Photon-photon gate via the interaction between two collective Rydberg excitations

We propose a scheme for a deterministic controlled-phase gate between two photons based on the strong interaction between two stationary collective Rydberg excitations in an atomic ensemble. The distance-dependent character of the interaction causes both a momentum displacement of the collective excitations and unwanted entanglement between them. We show that these effects can be overcome by swapping the collective excitations in space and by optimizing the geometry, resulting in a photon-photon gate with high fidelity and efficiency.

quant-ph↗