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Register a new userEnhancement of microwave squeezing via parametric down-conversion in a superconducting quantum circuit
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We propose an experimentally accessible superconducting quantum circuit, consisting of two coplanar waveguide resonators (CWRs), to enhance the microwave squeezing via parametric down-conversion (PDC). In our scheme, the two CWRs are nonlinearly coupled through a superconducting quantum interference device embedded in one of the CWRs. This is equivalent to replacing the transmission line in a flux-driven Josephson parametric amplifier (JPA) by a CWR, which makes it possible to drive the JPA by a quantized microwave field. Owing to this design, the PDC coefficient can be considerably increased to be about tens of megahertz, satisfying the strong-coupling condition. Using the Heisenberg-Langevin approach, we numerically show the enhancement of the microwave squeezing in our scheme. In contrast to the JPA, our proposed system becomes stable around the critical point and can generate stronger transient squeezing. In addition, the strong-coupling PDC can be used to engineer the photon blockade.
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Spontaneous Parametric Down-Conversion (SPDC), also known as parametric fluorescence, parametric noise, parametric scattering and all various combinations of the abbreviation SPDC, is a non-linear optical process where a photon spontaneously splits into two other photons of lower energies. One would think that this article is about particle physics and yet it is not, as this process can occur fairly easily on a day to day basis in an optics laboratory. Nowadays, SPDC is at the heart of many quantum optics experiments for applications in quantum cryptography, quantum simulation, quantum metrology but also for testing fundamentals laws of physics in quantum mechanics. In this article, we will focus on the physics of this process and highlight few important properties of SPDC. There will be two parts: a first theoretical one showing the particular quantum nature of SPDC and the second part, more experimental and in particular focusing on applications of parametric down-conversion. This is clearly a non-exhaustive article about parametric down-conversion as there is a tremendous literature on the subject, but it gives the necessary first elements needed for a novice student or researcher to work on SPDC sources of light.
By driving a dispersively coupled qubit-resonator system, we realize an impedance-matched $Lambda$ system that has two identical radiative decay rates from the top level and interacts with a semi-infinite waveguide. It has been predicted that a photon input from the waveguide deterministically induces a Raman transition in the system and switches its electronic state. We confirm this through microwave response to a continuous probe field, observing near-perfect ($99.7%$) extinction of the reflection and highly efficient ($74%$) frequency down-conversion. These proof-of-principle results lead to deterministic quantum gates between material qubits and microwave photons and open the possibility for scalable quantum networks interconnected with waveguide photons.
In a series of articles we have shown that all parametric-down- conversion processes, both of type-I and type-II, may be described by a positive Wigner density. These results, together with our description of how light detectors subtract the zeropoint radiation, indicated the possibility of a completely local realist theory of all these processes. In the present article we show how the down-converted fields may be described as retarded fields, generated by currents inside the nonlinear crystal, thereby achieving such a theory. Most of its predictions coincide with the standard nonlocal theory. However, the intensities of the down converted signals do not correspond exactly with the photon pairs of the nonlocal theory. For example, in a blue- red down conversion we would find 1.03 red photons for every blue one. The theory also predicts a new phenomenon, namely parametric up conversion from the vacuum.
Using different configurations of applied strong driving and weak probe fields, we find that only a single three-level superconducting quantum circuit (SQC) is enough to realize amplification, attenuation and frequency conversion of microwave fields. Such a three-level SQC has to possess $Delta$-type cyclic transitions. Different from the parametric amplification (attenuation) and frequency conversion in nonlinear optical media, the real energy levels of the three-level SQC are involved in the energy exchange when these processes are completed. We quantitatively discuss the effects of amplification (attenuation) and the frequency conversion for different types of driving fields. The optimal points are obtained for achieving the maximum amplification (attenuation) and conversion efficiency. Our study provides a new method to amplify (attenuate) microwave, realize frequency conversion, and also lay a foundation for generating single or entangled microwave photon states using a single three-level SQC.
In this Letter we describe a new two-mode system, which consists of Kerr-like medium and down conversion process, called the Kerr-down conversion system. Under a certain condition we can obtain an exact solution of the dynamical equations of motion. For this system we investigate different kinds of quadrature squeezing, e.g., single-mode, two-mode and sum-squeezing. Also we give a more general definition of the principal squeezing. We show that the amounts of nonclassical effects produced by the Kerr-like and down-conversion processes separately are greater than those obtained from the Kerr-down conversion system where both the processes are in competition.
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