Multiple-output microwave single-photon source using superconducting circuits with longitudinal and transverse couplings

Abstract

Single-photon devices at microwave frequencies are important for applications in quantum information processing and communication in the microwave regime. In this work, we describe a proposal of a multi-output single-photon device. We consider two superconducting resonators coupled to a gap-tunable qubit via both its longitudinal and transverse degrees of freedom. Thus, this qubitresonator coupling differs from the coupling in standard circuit quantum-electrodynamic systems described by the Jaynes-Cummings model. We demonstrate that an effective quadratic coupling between one of the normal modes and the qubit can be induced, and this induced second-order nonlinearity is much larger than that for conventional Kerr-type systems exhibiting photon blockade. Assuming that a coupled normal mode is resonantly driven, we observe that the output fields from the resonators exhibit strong sub-Poissonian photon-number statistics and photon antibunching. Contrary to previous studies on resonant photon blockade, the first-excited state of our device is a pure single-photon Fock state rather than a polariton state, i.e., a highly hybridized qubit-photon state. In addition, it is found that the optical state truncation caused by the strong qubit-induced nonlinearity can lead to an entanglement between the two resonators, even in their steady state under the Markov approximation.

Antibunching in an optomechanical oscillator

“…To this end, several recent proposals have studied possible nonlinearities in optomechanical setups exploiting, for example, an enhanced optomechanical nonlinearity based on an optomechanical system employing a few optical modes * hseok@kongju.ac.kr [25][26][27][28], an intrinsic mechanical nonlinearity [29,30], and the coupling of mechanical systems to a qubit [31,32].…”

Amplified and tunable transverse and longitudinal spin-photon coupling in hybrid circuit-QED

“…In this work we focus on the practical task of how to switch, in situ, between an amplified longitudinal [35][36][37][38][39][40] , and an amplified transverse coupling, by only modulating the coupling strength, and without changing the spin or cavity energies directly. With the former (amplified longitudinal coupling) one can realize fast high-fidelity readout 35 and qubit-qubit coupling 36 .…”

Observing pure effects of counter-rotating terms without ultrastrong coupling: A single photon can simultaneously excite two qubits

“…Moreover, is it really always reasonable to apply the RWA in dipole-field or dipole-dipole coupling systems, which are far way from the ultrastrong-coupling regime?Other interesting quantum processes are multiexcitation and emission in a QED system. The process that a two-level atom (molecule) absorbs two or more photons simultaneously has been widely discussed in many quantum platforms [14,22,23,31,32]. However, the inverse process (of a single photon splitting to excite two and more atoms) is rarely studied [33][34][35].Recently, Garziano et al[33] predicted that one photon can simultaneously excite two or more qubits.…”

“…The excitation-number-nonconserving terms in a QED system can lead to many interesting quantum effects [8,[17][18][19][20][21][22][23], such as three-photon resonances [24], the modification of the standard inputoutput relation [25,26], quantum phase transitions [27], frequency conversion [28], or the deterioration of photon each other via an antiferromagnetic dipole-dipole interaction. We show that, when the sum of two qubits transition frequencies is approximately equal to the resonator frequency, the counter-rotating terms in the dipole-dipole interaction cannot be dropped even when the system has not entered into the ultrastrong-coupling regime.…”

“…[33,36], the whole transition process proposed now only involves a single intermediate step, and the process rate can be much faster. Additionally, our proposal does not require to induce both longitudinal and transverse couplings [33], so the superconducting qubit can work at the optimal point and, thus, the pure-dephasing rate of the qubits can be effectively suppressed [22,23,37,38]. Moreover, we consider qubits instead of the qutrits studied in Ref.…”