The quantum Zeno effect can be used to implement quantum logic operations using single photons. It is shown here that similar effects occur in a resonant system subject to nonlinear dissipation, and that these effects can be used to implement classical logic and memory devices.
We have previously shown that the quantum Zeno effect can be used to implement quantum logic gates for quantum computing applications, where the Zeno effect was produced using a strong two-photon absorbing medium. Here we show that the Zeno effect can also be used to implement classical logic gates whose inputs and outputs are high-intensity fields (coherent states). The operation of the devices can be understood using a quasistatic analysis, and their switching times are calculated using a dynamic approach. The two-photon absorption coefficient of rubidium vapor is shown to allow operation of these devices at relatively low power levels.
Although two-photon absorption (TPA) is a nonlinear optical process, it is not typically considered a fundamental resource for optical quantum information processing (QIP). We have recently shown that TPA and the quantum Zeno effect can be used to make deterministic quantum logic devices (Zeno gates) from an otherwise linear optical system. In a Zeno gate, TPA is used to suppress the failure events that would normally occur in a linear optics device when multiple photons exit the device in the same optical mode. We have also recently shown that additional two-photon absorbing media can be used in a more conventional manner, along with a Zeno gate, to convert weak laser pulses into heralded single photon pulses. Sources of this kind could have many potential benefits; however, the use of detectors and classical switches could limit their scalability, and therefore their usefulness in larger QIP systems. Here we describe how TPA and Zeno gates alone could be used to make more efficient, and possibly scalable, single-photon sources. Because the Zeno gates also rely on TPA, we show that the only critical enabling resource for this approach is an efficient TPA medium.
We have previously shown that two-photon absorption and the quantum Zeno effect can be used to make deterministic quantum logic devices from an otherwise linear optical system. Here we show that this type of quantum Zeno gate can be used with additional two-photon absorbing media and weak laser pulses to make a heralded single photon source. A source of this kind is expected to have a number of practical advantages that make it well suited for large-scale quantum-information-processing applications.
Quantum logic operations can be implemented using nonlinear phase shifts (the Kerr effect) or the quantum Zeno effect based on strong two-photon absorption. Both approaches utilize three-level atoms, where the upper level is tuned on resonance for the Zeno gates and off-resonance for the nonlinear phase gates. The performance of nonlinear phase gates and Zeno gates are compared under conditions where the parameters of the resonant cavities and three-level atoms are the same in both cases. It is found that the expected performance is comparable for the two approaches, despite the apparent differences in the way they are implemented.
We show that the quantum Zeno effect can be used to suppress the failure events that would otherwise occur in a linear optics approach to quantum computing. From a practical viewpoint, that would allow the implementation of deterministic logic gates without the need for ancilla photons or high-efficiency detectors. We also show that the photons can behave as if they were fermions instead of bosons in the presence of a strong Zeno effect, which leads to an alternative paradigm for quantum computation.