arXiv subjects

Hesam Zandi

Publications and source records attributed to Hesam Zandi.

11 recordsLinked to original sources

arXiv2025

Implementing Grover Algorithm on Quantum Chip Architecture Optimized with QGHNN for Fidelity and Entanglement Preservation

This study introduces a superconducting quantum chip architecture designed to simultaneously preserve entanglement and readout fidelity, addressing one of the key trade-offs in the development of scalable quantum hardware. In conventional quantum circuits, strong qubit qubit coupling enhances entanglement but often leads to undesired crosstalk, dephasing, and reduced measurement fidelity. To mitigate these effects, we propose a hybrid multiqubit configuration consisting of nine transmon qubits organized into interior and exterior groups, interconnected via a flux tunable qubit and a network of distributed resonators. The interior qubits along with tunable qubit form an entanglement core, while the exterior qubits operate in the dispersive regime under large detuning to enable readout. The degree of entanglement can be dynamically tuned by adjusting the coupling between the central tunable qubit and the interior qubits. The total Hamiltonian includes all significant coupling contributions, encompassing effective exchange interactions among interior and exterior qubits, as well as their mediated couplings through interface resonators. By numerically solving the complete Hamiltonian alongside the Lindblad master equation, the system dynamics are characterized, allowing evaluation of both spectroscopic features and separation fidelity. Simulation results demonstrate that the proposed design maintains strong entanglement by creating the avoided-crossing region while sustaining measurement fidelity around 0.995 under realistic noise conditions. These findings confirm that entanglement strength and readout fidelity can be co-optimized within a single, reconfigurable architecture, establishing a viable route toward high-performance and scalable superconducting quantum processors.

quant-ph↗

arXiv2025

Trainmon: a framework for reverse engineering potentials in superconducting Qubits

A framework named Trainmon is introduced to reverse-engineer a quantum potential well for superconducting qubits. Trainmon consists of parallel branches of identical Josephson junctions. The Hamiltonian for this circuit resembles a discrete cosine transform, which can be applied to mimic various potentials. This framework is applied to well-known qubit potentials such as Quarton and Fluxonium, and their Hamiltonians are extracted and solved to validate the transition frequencies and calculate the coherence times of both the original qubits and their Trainmon-based versions.

quant-ph↗

arXiv2025

Technical Review on RF-Amplifiers for Quantum Computer Circuits: New Architectures of Josephson Parametric Amplifier

Josephson Parametric Amplifiers (JPAs) are key components in quantum information processing due to their ability to amplify weak quantum signals with near-quantum-limited noise performance. This is essential for applications such as qubit readout, quantum sensing, and communication, where signal fidelity and coherence preservation are critical. Unlike CMOS and HEMT amplifiers used in conventional RF systems, JPAs are specifically optimized for millikelvin (mK) cryogenic environments. CMOS amplifiers offer good integration but perform poorly at ultra-low temperatures due to high noise. HEMT amplifiers provide better noise performance but are power-intensive and less suited for mK operation. JPAs, by contrast, combine low power consumption with ultra-low noise and excellent cryogenic compatibility, making them ideal for quantum systems. The first part of this study compares these RF amplifier types and explains why JPAs are preferred in cryogenic quantum applications. The second part focuses on the design and analysis of JPAs based on both single Josephson junctions and junction arrays. While single-junction JPAs utilize nonlinear inductance for amplification, they suffer from gain compression, limited dynamic range, and sensitivity to fabrication variations. To overcome these challenges, this work explores JPA designs using Josephson junction arrays. Arrays distribute the nonlinear response, enhancing power handling, linearity, impedance tunability, and coherence while reducing phase noise. Several advanced JPA architectures are proposed, simulated, and compared using quantum theory and CAD tools to assess performance trade-offs and improvements over conventional designs.

quant-ph↗

arXiv2025

Design of Advanced Readout and System-on-Chip Analog Circuits for Quantum Chip

In this work, we design an advanced quantum readout architecture that integrates a four qubit superconducting chip with a novel parametric amplifier ended with analog front-end circuit. Unlike conventional approaches, this design eliminates the need for components such as Purcell filters. Instead, a Josephson Parametric Amplifier is engineered to simultaneously perform quantum-limited signal amplification and suppress qubit energy leakage. The design features a tailored gain profile across C-band, with sharp peaks (24 dB) and troughs (0 dB), enabling qubit frequencies to align with gain minima and resonator frequencies with gain maxima.

quant-ph↗

arXiv2024

Design of Qubit Readout Circuit for Purcell Rate Suppressing and Nonclassicality Enhancing

The Purcell effect, a common issue in qubit-resonator systems leading to both fidelity and nonclassicality losses is studied while its suppression is achieved using a novel qubit readout circuit design. Our approach utilizes a unique coupling architecture in which, the qubit first interacts with a filter resonator before coupling to the readout resonator. This configuration enables precise control over the Purcell decay rate and ac Stark factor without impacting on measuring time. The mentioned factor is highly sensitive to the coupling strength between the readout resonator and the filter, meaning that the factor adjustment directly impacts the qubit state detection. A major advantage of this design is that tuning the resonator-filter coupling strength is relatively straightforward, offering flexibility in fine-tuning ac Stark factor. This work extensively analyzes the system using full quantum mechanical theory, deriving the total Hamiltonian and investigates mode dynamics via quantum Langevin equations. Key parameters influencing the nonclassicality of output signals are also explored through quantum correlation metrics, including symplectic eigenvalues, quantum discord, and classical discord. The main goal is to find any compromises exsting between the ac Stark factor increasing and the quantum correlation created in the readout circuit. By optimizing the critical factors, by which the ac Stark factor mainly affected, the proposed design not only improves the distinguishability of the qubit states but also ensures robust nonclassicality in the output signals. Results demonstrate the potential of the proposed system to bridge the gap between a high fidelity readout and quantum correlation preservation in scalable quantum architectures.

quant-ph↗

arXiv2023

A Cost-Effective Test Bench for Evaluating Safe Human-Robot Interaction in Mobile Robotics

Safety concerns have risen as robots become more integrated into our daily lives and continue to interact closely with humans. One of the most crucial safety priorities is preventing collisions between robots and people walking nearby. Despite developing various algorithms to address this issue, evaluating their effectiveness on a cost-effective test bench remains a significant challenge. In this work, we propose a solution by introducing a simple yet functional platform that enables researchers and developers to assess how humans interact with mobile robots. This platform is designed to provide a quick yet accurate evaluation of the performance of safe interaction algorithms and make informed decisions for future development. The platform's features and structure are detailed, along with the initial testing results using two preliminary algorithms. The results obtained from the evaluation were consistent with theoretical calculations, demonstrating its effectiveness in assessing human-robot interaction. Our solution provides a preliminary yet reliable approach to ensure the safety of both robots and humans in their daily interactions.

cs.RO↗

arXiv2014

Precise Time Evolution of Superconductive Phase Qubits

New procedure on precise analysis of superconducting phase qubits using the concept of Feynman path integral in quantum mechanics and quantum field theory has been introduced. The wave function and imaginary part of the energy of the pseudo ground state of the Hamiltonian in phase qubits has been obtained from semi classical approximation and we we estimate decay rate, and thus the life time of meta stable using the approach of Instanton model. We devote the main effort to study the evolution of spectrum of Hamiltonian in time after addition of interaction Hamiltonian, in order to obtain the high fidelity quantum gates.

cond-mat.supr-con↗

arXiv2014

Fate of False Vacuum in Superconducting Flux Qubits

We propose a similarity between the scenario of fate of false vacuum in cosmology at early universe and the situation in where the quantum state decays in superconducting Flux qubit. This is due to the fact that both cases have two homogeneous stable equilibrium states in scalar field, which in quantum theory, could penetrate through the barrier in different possibilities and hence considered unstable decaying in time. In quantum computation, decay rate is among the most important factors in characteristics of the system like coherency, reliability, measurement fidelity, etc. In this considered potential, the decay rate from the penetrating (False vacuum) state to the stable (absolute minimum) state is achieved to leading order in Planck constant by the approach of Instanton model. In case of the superconducting flux qubit having thin barrier potential, the decay rate is calculated and its relations with actual set of parameters in flux qubit design are introduced.

cond-mat.supr-con↗

arXiv2014

Feynman Path Integral Approach on Superconducting Qubits and Readout Process

In this paper we introduce a new procedure on precise analysis of various physical manifestations in superconducting Qubits using the concept of Feynman path integral in quantum mechanics and quantum field theory. Three specific problem are discussed, we devote the main efforts to studying the wave function and imaginary part of the energy of the pseudo ground state of the Hamiltonian in Phase Qubits and we estimate decay rate, and thus the life time of meta stable states using the approach of 't Hooft's Instantons model. Correction to the Tilted-Washboard potential and current of Phase Qubits by precise analysis of Ginzburg-Landau's free energy equation has been considered. Also we evaluate the most accurate value of energy levels and wave function in Charge and Flux Qubits by Semi classical approximation in path integral formalism by considering limits of experimental errors, comparing them with WKB results and finally, we try to study more specific the evolution of spectrum of Hamiltonian in time after addition of interaction Hamiltonian, in order to obtain the high fidelity quantum gates.

quant-ph↗

arXiv2011

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

physics.optics↗

arXiv2010

Optimization of Junction and Bias Parameters in readout of Phase Qubit

The exact numerical solution of the nonlinear Ginzburg-Landau equation for Josephson junctions is obtained, from which the nontrivial current density and effective potential of the Josephson junction are accurately found. Tunneling probabilities of the calculated bound states in the resulting potential well are computed. The effects of junction and bias parameters such as thickness of the insulating barrier, cross sectional area, bias current and magnetic field are fully investigated using a successive perturbation approach. We define and compute figures of merit for achieving optimal operation of phase qubits and measurement of states. Particularly, it is predicted that Josephson junctions with thicker barriers yield better performance in measurement of the phase qubit. The proportion of other parameters is also studied and discussed for the right situation of the setup. Results are in complete agreement with reported experimental data.

cond-mat.supr-con↗