Circuit quantization from first principles

Superconducting circuit quantization conventionally starts from classical Euler-Lagrange circuit equations of motion. Invoking the correspondence principle yields a canonically quantized description of circuit dynamics over a bosonic Hilbert space. This approach has been very successful for describi...

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Main Authors: Yun-Chih Liao, Ben J. Powell, Thomas M. Stace
Format: Article
Language:English
Published: American Physical Society 2025-08-01
Series:Physical Review Research
Online Access:http://doi.org/10.1103/dfrq-44vk
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author Yun-Chih Liao
Ben J. Powell
Thomas M. Stace
author_facet Yun-Chih Liao
Ben J. Powell
Thomas M. Stace
author_sort Yun-Chih Liao
collection DOAJ
description Superconducting circuit quantization conventionally starts from classical Euler-Lagrange circuit equations of motion. Invoking the correspondence principle yields a canonically quantized description of circuit dynamics over a bosonic Hilbert space. This approach has been very successful for describing experiments, but implicitly starts from the classical Ginsberg-Landau mean-field theory for the circuit. Here, we employ a different approach that starts from a microscopic fermionic Hamiltonian for interacting electrons, whose ground space is described by the Bardeen-Cooper-Schrieffer (BCS) many-body wave function that underpins conventional superconductivity. We introduce the BCS ground space as a subspace of the full fermionic Hilbert space, and show that projecting the electronic Hamiltonian onto this subspace yields the standard Hamiltonian terms for Josephson junctions, capacitors, and inductors, from which standard quantized circuit models follow. This approach does not impose a spontaneously broken symmetry so that it consistently describes quantized circuits that support superpositions of phases, and the canonical commutation relations between phase and charge are derived from the underlying fermionic commutation properties, rather than imposed. By expanding the projective subspace, this approach can be extended to describe phenomena outside the BCS ground space, including quasiparticle excitations.
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spelling doaj-art-0d60248476df402f809fb63b07fc7dfa2025-08-20T03:03:15ZengAmerican Physical SocietyPhysical Review Research2643-15642025-08-017303314410.1103/dfrq-44vkCircuit quantization from first principlesYun-Chih LiaoBen J. PowellThomas M. StaceSuperconducting circuit quantization conventionally starts from classical Euler-Lagrange circuit equations of motion. Invoking the correspondence principle yields a canonically quantized description of circuit dynamics over a bosonic Hilbert space. This approach has been very successful for describing experiments, but implicitly starts from the classical Ginsberg-Landau mean-field theory for the circuit. Here, we employ a different approach that starts from a microscopic fermionic Hamiltonian for interacting electrons, whose ground space is described by the Bardeen-Cooper-Schrieffer (BCS) many-body wave function that underpins conventional superconductivity. We introduce the BCS ground space as a subspace of the full fermionic Hilbert space, and show that projecting the electronic Hamiltonian onto this subspace yields the standard Hamiltonian terms for Josephson junctions, capacitors, and inductors, from which standard quantized circuit models follow. This approach does not impose a spontaneously broken symmetry so that it consistently describes quantized circuits that support superpositions of phases, and the canonical commutation relations between phase and charge are derived from the underlying fermionic commutation properties, rather than imposed. By expanding the projective subspace, this approach can be extended to describe phenomena outside the BCS ground space, including quasiparticle excitations.http://doi.org/10.1103/dfrq-44vk
spellingShingle Yun-Chih Liao
Ben J. Powell
Thomas M. Stace
Circuit quantization from first principles
Physical Review Research
title Circuit quantization from first principles
title_full Circuit quantization from first principles
title_fullStr Circuit quantization from first principles
title_full_unstemmed Circuit quantization from first principles
title_short Circuit quantization from first principles
title_sort circuit quantization from first principles
url http://doi.org/10.1103/dfrq-44vk
work_keys_str_mv AT yunchihliao circuitquantizationfromfirstprinciples
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