Time‐resolved statistics of photon pairs in two‐cavity Josephson photonics

Abstract

We analyze the creation and emission of pairs of highly nonclassical microwave photons in a setup where a voltage‐biased Josephson junction is connected in series to two electromagnetic oscillators. Tuning the external voltage such that the Josephson frequency equals the sum of the two mode frequencies, each tunneling Cooper pair creates one additional photon in both of the two oscillators. The time‐resolved statistics of photon emission events from the two oscillators is investigated by means of single‐ and cross‐oscillator variants of the second‐order correlation function g(2)false(τfalse) and the waiting‐time distribution w(τ). They provide insight into the strongly correlated quantum dynamics of the two oscillator subsystems and reveal a rich variety of quantum features of light including strong antibunching and the presence of negative values in the Wigner function.

Waiting time distributions in a two-level fluctuator coupled to a superconducting charge detector

“…Electron waiting times have been investigated for a wide range of physical systems including quantum dots, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] coherent conductors, 36,37 molecular junctions, 38,39 and superconducting systems. [40][41][42][43][44][45][46] Distributions of waiting times contain complementary information on charge transport properties which is not necessarily encoded in the full counting statistics (FCS) and vice versa. 19 For example, waiting-time distributions capture the interference effects in double-dot setups, 20 reveal the correlations in multichannel systems, 24,47 allow to separate slow and fast dynamics in Cooper-pair splitters, 45 resolve few-photon processes, 48 and even investigate the topological superconductivity in hybrid junctions.…”

Generating entangled quantum microwaves in a Josephson-photonics device

“…A Josephson-photonics setup, as pioneered by the experimental groups at Saclay/Grenoble [21,25,26] and Dartmouth [22][23][24] and subsequently extensively investigated theoretically [23,[28][29][30][31][32][33][34][35][36][37][38][39][40][41], uses a Josephson junction biased by an external dc voltage V to create microwave excitations in two or more series-connected LC oscillators with frequencies w = L C 1 q q q , see figure 1(a). These oscillators parallel the microwave stripline cavities coupled to qubits in standard circuit-QED setups, where, however, there is no dc-current path through the system.…”

“…The similarity to the 2×2 case can be explained by the fact that, in consequence of energy conservation and the simultaneous creation of photons, the mean occupations of the two oscillators are coupled, g g á ñ = á ñ n n a a b b st st . The presence of the qubit thus leads to signatures of state-space restriction in the sixteen-level system (see [35,39]…”

“…The time-resolved statistics of photon emission events from the cavities has recently been studied experimentally and theoretically for Josephson-photonics setups [25][26][27][33][34][35][36][37][38]. Borrowing tools from quantum optics [58][59][60], in particular the second-order correlation function t ( ) ( ) g 2 , provides a deep insight into the strongly correlated quantum dynamics of the oscillator subsystems.…”

“…These are reachable in such systems since one can build on the immense research effort (and the resulting amazing progress in performance and control) which has been spent on these standard circuitquantum-electrodynamics (QED) setups as part of the larger quest for universal quantum computing. Here we argue, however, that combining two key elements of circuit-QED setups, namely, Josephson junctions and microwave cavities, in a much simpler, less demanding device can offer an alternative, fully tunable and versatile entanglement-generating source.Recently developed Josephson-photonics devices [21][22][23][24], which already demonstrated their potential as a source of nonclassical microwave light [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], seem to be logical candidates for this task. In fact, the next generation of setups currently being under fabrication is designed to explore bipartite photon creation processes.…”