Unconventional photon blockade in the two-photon Jaynes–Cummings model with two-frequency cavity drivings and atom driving

In a two-frequency cavity driving and atom driving atom-cavity system,we find the photon blockade effect.In a truncated eigenstates space,we calculate the zero-delay second-order correlation function of the cavity mode analytically and obtain an optimal condition for the photon blockade.By including three transition pathways,we find that higher excitations of the cavity mode can be further suppressed and the zero-delay second-order correlation function can be reduced additionally.Based on the master equation,we simulate the system evolution and find that the analytical solutions match well with the numerical results.Our scheme is robust with small fluctuations of parameters and may be used as a new type of single photon source.

Photon blockade in a cavity–atom optomechanical system

We study the single-photon blockade(1 PB),two-photon blockade(2 PB),and photon-induced tunneling(PIT)effects in a cavity–atom optomechanical system in which a two-level atom is coupled to a single-model cavity field via a twophoton interaction.By analyzing the eigenenergy spectrum of the system,we obtain a perfect 1 PB with a high occupancy probability of single-photon excitation,which means that a high-quality and efficient single-photon source can be generated.However,PIT often occurs in many cases when we consider 2 PB in analogy to 1 PB.In addition,we find that a 2 PB region will present in the optomechanical system,which can be proved by calculating the correlation function of the model analytically.

Unconventional photon blockade in a three-mode system with double second-order nonlinear coupling

The unconventional photon blockade(UPB)for low-frequency mode is investigated in a three-mode system with double second-order nonlinearity.By analyzing the Hamiltonian of the system,the optimal analytic condition of UPB in low-frequency mode is obtained.The numerical results are calculated by solving the master equation in a truncated Fock space,which agrees well with the analytic conditions.Through the numerical analysis of the system,it is found that the weak driving strength is favorable for the system to realize the UPB effect,and the system is insensitive to the changes of attenuation rate and environmental temperature.The comparison with the two-mode system and another similar threemode system shows that,under similar system parameters,the UPB effect of this double two-order nonlinear system is more obvious.

Manipulation of nonreciprocal unconventional photon blockade in a cavity-driven system composed of an asymmetrical cavity and two atoms with weak dipole–dipole interaction

We present a work of manipulating collective unconventional photon blockade(UCPB)and nonreciprocal UCPB(NUCPB)in a cavity-driven system composed of an asymmetrical single-mode cavity and two interacting identical twolevel atoms(TLAs).When the atoms do not interact directly,the frequency and intensity restrictions of collective UCPB can be specified,and a giant NUCPB exists due to the splitting of optimal atom–cavity coupling strength in proper parameter regime.However,if a weak atom–atom interaction which provides a new and feeble quantum interference pathway to UCPB is taken into account,two restrictions of UCPB are combined complexly,which are rigorous to be matched simultaneously.Due to the push-and-pull effect induced by weak dipole–dipole interaction,the UCPB regime is compressed more or less.NUCPB is improved as a higher contrast is present when the two complex UCPB restrictions are matched,while it is suppressed when the restrictions are mismatched.In general,whether NUCPB is suppressed or promoted depends on its working parameters.Our findings show a prospective access to produce giant quantum nonreciprocity by a couple of weakly interacting atoms.

Unconventional photon blockade induced by the self-Kerr and cross-Kerr nonlinearities

We study the use of the self-Kerr and cross-Kerr nonlinearities to realize strong photon blockade in a weakly driven,four-mode optomechanical system.According to the Born–Oppenheimer approximation,we obtain the cavity self-Kerr coupling and the inter-cavity cross-Kerr coupling,adiabatically separated from the mechanical oscillator.Through minimizing the second-order correlation function,we find out the optimal parameter conditions for the unconventional photon blockade.Under the optimal conditions,the strong photon blockade can appear in the strong or weak nonlinearities.

Phase-controlled photon blockade in optomechanical systems

The manipulation of photons is a key technology for obtaining optical quantum information.In this study,we present a phase-modulated optomechanical system comprising two coupled cavity resonators and illustrate the phase-controlled photon blockade in the system.The coupling phase of the cavities reveals the interference of photons and introduces an unconventional photon-blockade effect.We also study the influence of the energy level fineness on the photon blockade and resonant frequency of the mechanical mode.Numerical simulations demonstrate that photon blockade can occur over a wide range of system parameters.These results have several implications for understanding the role of the state phase in quantum cavity optomechanics and provide a promising method for the realization of optomechanical quantum devices using photon blockade.

Nonreciprocal photon blockade in a spinning resonator coupled to two two-level atoms

We propose a scheme to simultaneously achieve nonreciprocal conventional photon blockade(NCPB) and unconventional photon blockade(NUPB) in a spinning resonator coupled to two two-level atoms. We show that, with the unequal frequency detuning of cavity and atoms from the driving laser, the quantum efect of the nonreciprocal photon blockade can be realized based on two regimes under diferent driving strengths. We confirm that, the NUPB results from the quantum destructive interference between distinct pathways when the driving laser is loaded from one side, whereas the destructive interference is broken when the system is driven from the other side. Moreover, the NCPB originates from whether the single excitation resonance condition is satisfied, corresponding to the opposite driving direction in contrast to the former. Besides, we obtain the optimal nonreciprocal results by appropriately choosing the system parameters. Interestingly, the UPB exhibits stronger robustness to thermal noises,and the nonreciprocity still exists up to a high thermal excitation. This work provides an alternative way to achieve nonreciprocal quantum devices based on the nonreciprocal photon blockade, which may help to develop information network processing.

Quantum fluctuation and interference effect in a single atom-cavity QED system driven by a broadband squeezed vacuum

Squeezed vacuum, as a nonclassical field, has many interesting properties and results in many potential applications for quantum measurement and information processing. Here, we investigate a single atom–cavity quantum electrodynamics(QED) system driven by a broadband squeezed vacuum. In the presence of the atom, we show that both the mean photon number and the quantum fluctuations of photons in the cavity undergo a significant depletion due to the additional transition pathways generated by the atom–cavity interaction.By measuring these features, one can detect the existence of atoms in the cavity. We also show that two-photon excitation can be significantly suppressed by the quantum destructive interference when the squeezing parameter is very small. These results presented here are helpful in understanding the quantum nature of the broadband squeezed vacuum.

Spinning microresonator-induced chiral optical transmission

Chiral quantum optics is a new research area in light-matter interaction that depends on the direction of light propagation and offers a new path for the quantum regulation of light-matter interactions.In this paper,we study a spinning Kerr-type microresonator coupled withΛ-type atom ensembles,which are driven in opposite directions to generate asymmetric photon statistics.We find that a photon blockade can only be generated by driving the spinning resonator on right side without driving the spinning microresonator from the left side,resulting in chirality.The coupling strength between system modes can be precisely controlled by adjusting the detuning amount of the atomic pump field.Because of the splitting of the resonant frequency generated by the Fizeau drag,the destructive quantum interference generated in right side drive prevents the nonresonant transition path of state|1,0⟩to state|2,0⟩.This direction-dependent chiral quantum optics is expected to be applied to chiral optical devices,single-photon sources and nonreciprocal quantum communications.