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International Conference on Noise and Fluctuations

Vacuum-noise-induced multimode correlations in a superconducting cavity

Pasi Lähteenmäki, Gheorghe Sorin Paraoanu, Pertti Juhani Hakonen

Published Jun 1, 2017• 1 citation
Publisher

Abstract

We recently presented [1] experimental results on multimode correlations obtained from pumped superconducting microwave cavity cooled down to its ground state. These correlations originate from an interaction of the pump field with the quantum fluctuations of vacuum in the cavity which includes a pump-amplitude-dependent reactance. In this paper we discuss the nature of the created multimode correlations with the help of a semiclassical simulation carried out in the time domain. In the simulation based on the Heisenberg-Langevin equation of motion, quantum noise is approximated as white noise over small ranges of frequency.

DOI
10.1109/icnf.2017.7985937

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We recently presented [1] experimental results on multimode correlations obtained from pumped superconducting microwave cavity cooled down to its ground state. These correlations originate from an interaction of the pump field with the quantum fluctuations of vacuum in the cavity which includes a pump-amplitude-dependent reactance. In this paper we discuss the nature of the created multimode correlations with the help of a semiclassical simulation carried out in the time domain. In the simulation based on the Heisenberg-Langevin equation of motion, quantum noise is approximated as white noise over small ranges of frequency.
The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity, it is possible to generate another type of correlation, namely coherence between photons in separate frequency modes. The coherence correlations are tunable by the phases of the pumps and are established by a quantum fluctuation that stimulates the simultaneous creation of two photon pairs. Our analysis indicates that the origin of this vacuum-induced coherence is the absence of which-way information in the frequency space.
Quantum correlations are an essential resource in advanced information processing based on quantum phenomena. Remarkably, the vacuum state of a quantum field may act as a key element for generation of strong quantum correlations. Besides, superconducting microwave cavities offer an excellent platform for experimental studies of such quantum effects. In this work, we numerically investigate vacuum correlations in a flux-tunable superconducting cavity under multiple pump tones. We consider double and triple pumping cases and explore pairwise correlations between three frequency bands specified within a single cavity resonance. Our work shows that three pumps produce more correlations than two pumps; thus, quantum resources facilitated by the triple pump scheme offers enhanced prospects for quantum data processing using parametric microwave cavities.
We present a systematic semiclassical model for the simulation of the dynamics of a single two-level atom strongly coupled to a driven high-finesse optical cavity. From the Fokker-Planck equation of the combined atom-field Wigner function we derive stochastic differential equations for the atomic motion and the cavity field. The corresponding noise sources exhibit strong correlations between the atomic momentum fluctuations and the noise in the phase quadrature of the cavity field. The model provides an effective tool to investigate localisation effects as well as cooling and trapping times. In addition, we can continuously study the transition from a few photon quantum field to the classical limit of a large coherent field amplitude.
We present a systematic semiclassical model for the simulation of the dynamics of a single two-level atom strongly coupled to a driven high-finesse optical cavity.From the Fokker-Planck equation of the combined atom-field Wigner function we derive stochastic differential equations for the atomic motion and the cavity field.The corresponding noise sources exhibit strong correlations between the atomic momentum fluctuations and the noise in the phase quadrature of the cavity field.The model provides an effective tool to investigate localization effects as well as cooling and trapping times.In addition, we can continuously study the transition from a few-photon quantum field to the classical limit of a large coherent field amplitude.
This thesis work deals with a range of superconducting devices operated near the fundamental performance limits set by quantum mechanics along with the nature of quantum vacuum itself when perturbed by such devices. These devices are operated in a dilution refrigerator cooled down to sub-Kelvin temperatures. Low temperature is absolutely essential for quantum behavior of these devices and the minimal inherent noise contribution. Biased, selectively damped superconducting tunnel junction, (also known as the Josephson junction) displaying negative differential resistance, was employed to construct a device capable of amplifying weak microwave signal reflections from it. This device can be operated near the intrinsic precision limits set by the Heisenberg's uncertainty principle. Arrays of Superconducting Quantum Interference Devices (SQUIDs), operated below the critical current, can be used for metamaterial resonators whose resonant frequency can be quickly modulated by magnetic flux. These devices are operated as parametric amplifiers and they are capable of amplifying weak microwave signals near the quantum limit of noise. But more importantly, they are capable of perturbing the vacuum itself, which creates correlated photon pairs seeded by vacuum fluctuations. This effect is known as the dynamical Casimir effect (DCE) and is demonstrated in this thesis work by using power and correlation measurements at microwave frequencies. Furthermore, investigations on the DCE have been extended using a double modulation scheme yielding vacuum-induced coherence and tripartite correlations. Nanocarbon devices have also been studied in this thesis, in particular a wideband low noise nanotube electrometer constructed from a nanotube with proximity induced superconductivity. This device has certain unique benefits when operated in a microwave environment which are discussed in the thesis. Another nanocarbon device, a double quantum dot constructed from graphene and superconducting leads has been used to demonstrate Cooper-pair splitting. This device operates as a tunable source of entangled electrons.
Recent quantum technologies have established precise quantum control of various microscopic systems using electromagnetic waves. Interfaces based on cryogenic cavity electro-optic systems are particularly promising, due to the direct interaction between microwave and optical fields in the quantum regime. Quantum optical control of superconducting microwave circuits has been precluded so far due to the weak electro-optical coupling as well as quasi-particles induced by the pump laser. Here we report the coherent control of a superconducting microwave cavity using laser pulses in a multimode electro-optical device at millikelvin temperature with near-unity cooperativity. Both the stationary and instantaneous responses of the microwave and optical modes comply with the coherent electro-optical interaction, and reveal only minuscule amount of excess back-action with an unanticipated time delay. Our demonstration enables wide ranges of applications beyond quantum transductions, from squeezing and quantum non-demolition measurements of microwave fields, to entanglement generation and hybrid quantum networks.