This doctorate thesis focuses on the effects of the electromagnetic environment on applied electromagnetic fields in single small junctions as well as arrays. We apply radio-frequency (RF) microwaves in the sub-gigahertz frequency range on a one-dimensional array of small Josephson junctions exhibiting distinct Coulomb blockade characteristics. We observed a gradual lifting of Coulomb blockade with increase in the microwave power which we interpret is due to photon-assisted tunneling of Cooper pairs in the classical (multi-photon absorption) regime. We observe that, due to its high sensitivity to microwave power, the array is well-suited for in situ microwave detection applications in low temperature environments. A detailed analysis of the characteristics in the classical (multi-photon absorption) limit reveals that the microwave amplitude is rescaled (renormalized), which we attribute to the difference in dc and ac voltage response of the array. We proceed to rigorously consider the origin of the aforementioned renormalization effect by considering the effect of the electromagnetic environment of the Josephson junction on applied oscillating voltages. We theoretically demonstrate that its effect is simply to renormalize the amplitude of oscillation in a predictable manner traced to the physics of wave function renormalization (Lehmann weights) consistent with circuit-QED. We also introduce Einstein's A and B coefficients for small Josephson junctions, in a bid to relate the renormalization effect to the modification of photon absorption and emission amplitudes. Such renormalization implies that the sensitivity of the single junction and the array to oscillating electromagnetic fields (e.g. microwaves) is modulated and depends on the environmental impedance. The renormalization effect can be exploited to configure `opaque', `translucent' or `transparent' quantum circuits to microwaves.This doctorate thesis focuses on the effects of the electromagnetic environment on applied electromagnetic fields in single small junctions as well as arrays. We apply radio-frequency (RF) microwaves in the sub-gigahertz frequency range on a one-dimensional array of small Josephson junctions exhibiting distinct Coulomb blockade characteristics. We observed a gradual lifting of Coulomb blockade with increase in the microwave power which we interpret is due to photon-assisted tunneling of Cooper pairs in the classical (multi-photon absorption) regime. We observe that, due to its high sensitivity to microwave power, the array is well-suited for in situ microwave detection applications in low temperature environments. A detailed analysis of the characteristics in the classical (multi-photon absorption) limit reveals that the microwave amplitude is rescaled (renormalized), which we attribute to the difference in dc and ac voltage response of the array. We proceed to rigorously consider the origin of the aforementioned renormalization effect by considering the effect of the electromagnetic environment of the Josephson junction on applied oscillating voltages. We theoretically demonstrate that its effect is simply to renormalize the amplitude of oscillation in a predictable manner traced to the physics of wave function renormalization (Lehmann weights) consistent with circuit-QED. We also introduce Einstein's A and B coefficients for small Josephson junctions, in a bid to relate the renormalization effect to the modification of photon absorption and emission amplitudes. Such renormalization implies that the sensitivity of the single junction and the array to oscillating electromagnetic fields (e.g. microwaves) is modulated and depends on the environmental impedance. The renormalization effect can be exploited to configure `opaque', `translucent' or `transparent' quantum circuits to microwaves.

arXiv:2109.02440Sep 1, 20217 citations

Investigation of Microwave Radiation Emitted by Josephson Junctions

D. N. Langenberg, Douglas J. Scalapino, Barry N. Taylor +1 more

Physical Review LettersNov 22, 196511 citations

Non-classical light from superconducting resonators coupled to voltage-biased Josephson junctions

Björn Kubala, Vera Gramich, Joachim Ankerhold

The interplay of the tunneling transfer of charges and the emission and absorption of light can be investigated in a set-up, where a voltage-biased Josephson junction is placed in series to a microwave cavity. Here, we concentrate on the emission process and show that due to the inherent nonlinearity of the Josephson junction tunneling Cooper-pairs can create a variety of non-classical states of light. Depending on experimental parameters and tuning the device can be described by effective Hamiltonians, indicating specific photon creation mechanisms which lead to strongly bunched or anti-bunched light emission. We derive explicit analytical expressions for the photon correlation function $g^{(2)}(τ=0)$ for these different processes and investigate their full crossover numerically. Photon distribution functions show squeezing and other interesting non-Poissonian behavior.The interplay of the tunneling transfer of charges and the emission and absorption of light can be investigated in a set-up, where a voltage-biased Josephson junction is placed in series to a microwave cavity. Here, we concentrate on the emission process and show that due to the inherent nonlinearity of the Josephson junction tunneling Cooper-pairs can create a variety of non-classical states of light. Depending on experimental parameters and tuning the device can be described by effective Hamiltonians, indicating specific photon creation mechanisms which lead to strongly bunched or anti-bunched light emission. We derive explicit analytical expressions for the photon correlation function $g^{(2)}(τ=0)$ for these different processes and investigate their full crossover numerically. Photon distribution functions show squeezing and other interesting non-Poissonian behavior.

arXiv:1404.6259Physica ScriptaOct 1, 201529 citations

Investigation of Microwave Radiation Emitted by Josephson Junctions

D. N. Langenberg, Douglas J. Scalapino, Barry N. Taylor +1 more

Physical Review LettersAug 16, 1965148 citations

Constant-voltage steps in arrays of Nb-PdAu-Nb Josephson junctions

Samuel P. Benz, Charles J. Burroughs

Design and fabrication of Nb-PdAu-Nb trilayer Josephson junctions are described. The microwave response of an array of 1000 of these junctions was measured, and constant-voltage step heights mere characterized as a function of the microwave amplitude and frequency. Experimental results fit well to point-junction simulations at the 3 GHz design frequency of the microwave distribution network. The observed step height of 3.8 mA shows that the array and microwave distribution are sufficiently uniform for application in programmable Josephson voltage standards.Design and fabrication of Nb-PdAu-Nb trilayer Josephson junctions are described. The microwave response of an array of 1000 of these junctions was measured, and constant-voltage step heights mere characterized as a function of the microwave amplitude and frequency. Experimental results fit well to point-junction simulations at the 3 GHz design frequency of the microwave distribution network. The observed step height of 3.8 mA shows that the array and microwave distribution are sufficiently uniform for application in programmable Josephson voltage standards.

IEEE Transactions on Applied SuperconductivityJun 1, 199724 citations

g^{(2)}(τ=0)

for these different processes and investigate their full crossover numerically. Photon distribution functions show squeezing and other interesting non-Poissonian behavior.