Excited states of coherent harmonic qubits with long-range photon coupling and dissipation
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866912589942882304 |
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| author | Gamberale, L. Modanese, G. |
| author_facet | Gamberale, L. Modanese, G. |
| contents | It is known that ensembles of interacting oscillators or qubits can exhibit the phenomenon of quantum synchronization. In this work we consider a set of $N$ identical two-state systems that we call ``harmonic qubits'', because the kinetic part of their Hamiltonian is of the form $ω_0 \sum_i a^\dagger_i a_i$, coupled through a multi-state ``photon'' mode subject to dissipation. It has been proven numerically that when the coupling between the qubits and the photon is sufficiently strong, the ensemble condenses into a ground state with negative energy, the energy gap is proportional to $N$ and there are clear cross correlations $\langle a^\dagger_i a_j \rangle$. Here we are interested into the energy spectrum of the excited states of this system. In order to obtain information on the coherent transitions we introduce a weak coupling of each qubit with an external oscillator of variable frequency $ω$ and we check via Monte Carlo time evolution for which values of $ω$ variations in the occupation of the external oscillator occur. After adding a second external oscillator coupled to the first only through the $N$ qubits, we also look at the energy transfer between the two external oscillators in dependence on their frequency, a transfer which is possible only through the excited states of the qubits. Above threshold (when $E_0<0$) we find resonant transfer at frequencies which are definitely higher, and growing with $N$. This signals the presence of collective excited states, separated by large energy gaps, which are absent below threshold. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_05247 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Excited states of coherent harmonic qubits with long-range photon coupling and dissipation Gamberale, L. Modanese, G. General Physics It is known that ensembles of interacting oscillators or qubits can exhibit the phenomenon of quantum synchronization. In this work we consider a set of $N$ identical two-state systems that we call ``harmonic qubits'', because the kinetic part of their Hamiltonian is of the form $ω_0 \sum_i a^\dagger_i a_i$, coupled through a multi-state ``photon'' mode subject to dissipation. It has been proven numerically that when the coupling between the qubits and the photon is sufficiently strong, the ensemble condenses into a ground state with negative energy, the energy gap is proportional to $N$ and there are clear cross correlations $\langle a^\dagger_i a_j \rangle$. Here we are interested into the energy spectrum of the excited states of this system. In order to obtain information on the coherent transitions we introduce a weak coupling of each qubit with an external oscillator of variable frequency $ω$ and we check via Monte Carlo time evolution for which values of $ω$ variations in the occupation of the external oscillator occur. After adding a second external oscillator coupled to the first only through the $N$ qubits, we also look at the energy transfer between the two external oscillators in dependence on their frequency, a transfer which is possible only through the excited states of the qubits. Above threshold (when $E_0<0$) we find resonant transfer at frequencies which are definitely higher, and growing with $N$. This signals the presence of collective excited states, separated by large energy gaps, which are absent below threshold. |
| title | Excited states of coherent harmonic qubits with long-range photon coupling and dissipation |
| topic | General Physics |
| url | https://arxiv.org/abs/2502.05247 |