arXiv subjects

M. H. Ansari

Publications and source records attributed to M. H. Ansari.

6 recordsLinked to original sources

arXiv2024

Fast Gates of Detuned Cat Qubit

Cat qubits have emerged as a promising candidate for quantum computation due to their higher error-correction thresholds and low resource overheads. In existing literature, the detuning of the two-photon drive is assumed to be zero for implementing single and multi-qubit gates. We explore a modification of the Hamiltonian for a range of detuning and demonstrate that high fidelity single qubit gates can be performed even by proper parameter matching. We also analyze the CNOT gate in presence of an approximate detuning term and explain its fidelity improvements through Shortcut to Adiabaticity corrections.

quant-ph↗

arXiv2024

Entangling interactions between artificial atoms mediated by a multimode left-handed superconducting ring resonator

Superconducting metamaterial transmission lines implemented with lumped circuit elements can exhibit left-handed dispersion, where the group and phase velocity have opposite sign, in a frequency range relevant for superconducting artificial atoms. Forming such a metamaterial transmission line into a ring and coupling it to qubits at different points around the ring results in a multimode bus resonator with a compact footprint. Using flux-tunable qubits, we characterize and theoretically model the variation in the coupling strength between the two qubits and each of the ring resonator modes. Although the qubits have negligible direct coupling between them, their interactions with the multimode ring resonator result in both a transverse exchange coupling and a higher order $ZZ$ interaction between the qubits. As we vary the detuning between the qubits and their frequency relative to the ring resonator modes, we observe significant variations in both of these inter-qubit interactions, including zero crossings and changes of sign. The ability to modulate interaction terms such as the $ZZ$ scale between zero and large values for small changes in qubit frequency provides a promising pathway for implementing entangling gates in a system capable of hosting many qubits.

quant-ph↗

arXiv2022

Parasitic-free gate: A protected switch between idle and entangled states

We propose a gate to switch superconducting qubit pairs in and out of a two-body interaction. This gate uses cross resonance driving on a tunable circuit with adjusted parameters and without accumulating residual ZZ interaction for idle and interacting qubits. It is imperative that this gate does not spread errors through the quantum register. Our detailed theoretical results show that these error-free modes do not necessarily require largely tunable circuits, such as magnetic modulation of qubits or couplers. We obtain the operational gate on weakly tuneable circuits as well and show that switching between them is remarkably fast.

quant-ph↗

arXiv2021

ZZ freedom in two qubit gates

Superconducting qubits on a circuit exhibit an always-on state-dependent phase error. This error is due to sub-MHz parasitic interaction that repels computational levels from non-computational ones. We study a general theory to evaluate the `static' repulsion between seemingly idle qubits as well as the `dynamical' repulsion between entangled qubits under microwave driving gate. By combining qubits of either the same or opposite anharmonicity signs we find the characteristics of static and dynamical ZZ freedoms. The latter universally eliminate the parasitic repulsion, leading us to mitigate high fidelity gate operation. Our theory introduces new opportunities for making perfect entangled and unentangled states which is extremely useful for quantum technology.

quant-ph↗

arXiv2014

Dynamics of parametric fluctuations induced by quasiparticle tunneling in superconducting flux qubits

We present experiments on the dynamics of a two-state parametric fluctuator in a superconducting flux qubit. In spectroscopic measurements, the fluctuator manifests itself as a doublet line. When the qubit is excited in resonance with one of the two doublet lines, the correlation of readout results exhibits an exponential time decay which provides a measure of the fluctuator transition rate. The rate increases with temperature in the interval 40 to 158 mK. Based on the magnitude of the transition rate and the doublet line splitting we conclude that the fluctuation is induced by quasiparticle tunneling. These results demonstrate the importance of considering quasiparticles as a source of decoherence in flux qubits.

cond-mat.mes-hall↗

arXiv2014

Towards Tripartite Hybrid Entanglement in Quantum Dot Molecules

Establishing the hybrid entanglement among a growing number of matter and photonic quantum bits is necessary for the scalable quantum computation and long distance quantum communication. Here we demonstrate that charged excitonic complexes forming in strongly correlated quantum dot molecules are able to generate tripartite hybrid entanglement under proper carrier quantization. The mixed orbitals of the molecule construct multilevel ground states with sub-meV hole tunneling energy and relatively large electron hybridization energy. We show that appropriate size and interdot spacing maintains the electron particle weakly localized, opening extra recombination channels by correlating ground-state excitons. This allows for creation of higher order entangled states. Nontrivial hole tunneling energy, renormalized by the multi-particle interactions, facilitates realizing the energy coincidence among only certain components of the molecule optical spectrum. This translates to the emergence of favorable spectral components in a multi-body excitonic complex which sustain principal oscillator strengths throughout the electric-field-induced hole tunneling process. We particularly analyse whether the level broadening of favorable spin configurations could be manipulated to eliminate the distinguishability of photons.

cond-mat.mes-hall↗