We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feddback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum mechanics. We give a description of this measurement device as a quantum network scattering quantum fluctuations from input to output ports.
Relating the Glauber-Sudarshan, Wigner and Husimi quasiprobability distributions operationally through the quantum limited amplifier and attenuator channels
In an ideal linear amplifier, the output signal is linearly related to the input signal with an additive noise that is independent of the input. The decoherence of a quantum-mechanical state as a result of optical amplification is usually assumed to be due to the addition of quantum noise. Here we show that entanglement between the input signal and the amplifying medium can produce an exponentially-large amount of decoherence in an ideal optical amplifier even when the gain is arbitrarily close to unity and the added noise is negligible. These effects occur for macroscopic superposition states…
A Josephson parametric amplifier (JPA) is executed in a three-dimensional (3D) microwave cavity by coupling it to a superconducting quantum interference device (SQUID) that is embedded in a two-dimensional resonator. The JPA is activated in a three-wave mixing configuration by injecting ac magnetic flux, at twice the 3D cavity frequency, into the SQUID. An 8.3 GHz cavity is measured in a non-degenerate phase-insensitive configuration which yields gains in excess of 40 dB, where a 20 dB gain results in an operational bandwidth of 0.4 MHz, a 1 dB compression point of -115 dBm with half a quantum…
Nonlinear amplifiers such as the transistor are ubiquitous in classical technology, but their quantum analogues are not well understood. We introduce a class of nonlinear amplifiers that amplify any normal operator and add only a half-quantum of vacuum noise at the output. In the large-gain limit, when used in conjunction with a noisy linear detector, these amplifiers implement ideal measurements of the normal operator.
The act of observing a quantum object fundamentally perturbs its state, resulting in a random walk toward an eigenstate of the measurement operator. Ideally, the measurement is responsible for all dephasing of the quantum state. In practice, imperfections in the measurement apparatus limit or corrupt the flow of information required for quantum feedback protocols, an effect quantified by the measurement efficiency. Here we demonstrate the efficient measurement of a superconducting qubit using a nonreciprocal parametric amplifier to directly monitor the microwave field of a readout cavity. By m…
Josephson parametric amplifiers have emerged as a promising platform for quantum information processing and squeezed quantum states generation. Travelling wave and impedance-matched parametric amplifiers provide broad bandwidth for high-fidelity single-shot readout of multiple qubit superconducting circuits. Here, we present a quantum-limited 3-wave-mixing parametric amplifier based on superconducting nonlinear asymmetric inductive elements (SNAILs), whose useful bandwidth is enhanced with an on-chip two-section impedance-matching circuit based on microstrip transmission lines. The amplifier d…
Degenerate parametric amplifiers (DPAs) exhibit the unique property of phase-sensitive gain and can be used to noiselessly amplify small signals or squeeze field fluctuations beneath the vacuum level. In the microwave domain, these amplifiers have been utilized to measure qubits in elementary quantum processors, search for dark matter, facilitate high-sensitivity spin resonance spectroscopy and have even been proposed as the building blocks for a measurement based quantum computer. Until now, microwave DPAs have almost exclusively been made from nonlinear Josephson junctions, which exhibit hig…
We address quantum $M$-ary phase-shift keyed (PSK) communication channels in the presence of phase diffusion, and analyze the use of probabilistic noiseless linear amplifiers (NLA) to enhance performance of coherent signals. We consider both static and dynamical phase diffusion and assess the performances of the channel for ideal and realistic phase receivers. Our results show that NLA employed at the stage of signal preparations is a useful resource, especially in the regime of weak signals. We also discuss the interplay between the use of NLA, and the memory effects occurring with dynamical …
Simultaneous ideal quantum measurements of multiple single-photon-level signals would advance applications in quantum information processing, metrology, and astronomy, but require the first amplifier to be simultaneously broadband, quantum limited, and directional. However, conventional traveling-wave parametric amplifiers support broadband amplification at the cost of increased added noise and are not genuinely directional due to non-negligible nonlinear backward wave generation. In this work, we introduce a new class of amplifiers which encode the information in the Floquet modes of the syst…
The measurement of a quantum system is often performed by encoding its state in a single observable of a light field. The measurement efficiency of this observable can be reduced by loss or excess noise on the way to the detector. Even a \textit{quantum-limited} detector that simultaneously measures a second non-commuting observable would double the output noise, therefore limiting the efficiency to $50\%$. At microwave frequencies, an ideal measurement efficiency can be achieved by noiselessly amplifying the information-carrying quadrature of the light field, but this has remained an experime…
Single-mode Josephson junction-based parametric amplifiers are often modeled as perfect amplifiers and squeezers. We show that, in practice, the gain, quantum efficiency, and output field squeezing of these devices are limited by usually neglected higher-order corrections to the idealized model. To arrive at this result, we derive the leading corrections to the lumped-element Josephson parametric amplifier of three common pumping schemes: monochromatic current pump, bichromatic current pump, and monochromatic flux pump. We show that the leading correction for the last two schemes is a single K…
In the context of von Neumann projective measurement scenario for a qubit system, it is widely believed that the mutual orthogonality between the post-interaction pointer states is the sufficient condition for achieving the ideal measurement situation. However, for experimentally verifying the observable probabilities, the real space distinction between the pointer distributions corresponding to post-interaction pointer states play crucial role. It is implicitly assumed that mutual orthogonality ensures the support between the post-interaction pointer distributions to be disjoint. We point out…
The phase of an optical field inside a linear amplifier is widely known to diffuse with a diffusion coefficient that is inversely proportional to the photon number. The same process occurs in lasers which limits its intrinsic linewidth and makes the phase uncertainty difficult to calculate. The most commonly used simplification is to assume a narrow photon-number distribution for the optical field (which we call the small-noise approximation). For coherent light, this condition is determined by the average photon number. The small-noise approximation relies on (i) the input to have a good sign…
Detection of low-reflectivity objects can be enriched via the so-called quantum illumination procedure. In order that this quantum procedure outperforms classical detection protocols, entangled states of microwave radiation are initially required. In this paper, we discuss the role of Josephson Traveling Wave Parametric Amplifiers (JTWPAs), based on circuit-QED components, as suitable sources of a two-mode squeezed vacuum state, a special signal-idler entangled state. The obtained wide bandwidth makes the JTWPA an ideal candidate for generating quantum radiation in quantum metrology and inform…
University of Rochester（罗切斯特大学）；Institute for Quantum Studies, Chapman University（查普曼大学量子研究所）；University of California at Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
A combined ferrite parametric amplifier and millimeter-wave homodyne interferometer are proposed as an ambient temperature Bell Test. It is shown that the non-linear magnetic susceptibility of the yttrium iron garnet (YIG) ferrite, on account of its narrow line-width Larmor precessional resonance, make it an ideal material for the creation of entangled photons. These can be measured using a homodyne interferometer, as the much larger number of thermally generated photons associated with ambient temperature emission can be screened out. The proposed architecture may enable YIG quantum technolog…
A near-quantum-limited diamond maser amplifier operating at millikelvin temperatures
Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）；National Tsing Hua University（国立清华大学）；Delft University of Technology（代尔夫特理工大学）；QuTech and Kavli Institute of Nanoscience（QuTech与卡弗里纳米科学研究所）；Liquid Instruments（液体仪器公司）；Brown University（布朗大学）
Barnett Effect-Induced Nonreciprocal Entanglement and Gaussian interferometric power in Magnomechanics with Optical Parametric Amplifier
Ibnou Zohr University（伊本·佐赫尔大学）；Quaid-i-Azam University（奎德·阿扎姆大学）；Prince Sattam bin Abdulaziz University（沙特王子萨塔姆·本·阿卜杜勒阿齐兹大学）；Al-Ahliyya Amman University（安曼阿赫利耶大学）；King Khalid University（国王哈立德国王大学）；Islamic University of Madinah（麦地那伊斯兰大学）；University of Bisha（比沙大学）
The ability to induce, observe and control quantum coherent interactions in room temperature, electrically driven optoelectronic devices is of outmost significance for advancing quantum science and engineering towards practical applications. We demonstrate here a quantum interference phenomena, Ramsey fringes, in an inhomogeneously broadened InAs/InP quantum dot (QD) ensemble in the form of a 1.5 mm long optical amplifier operating at room temperature. Observation of Ramsey fringes in semiconductor QD was previously achieved only at cryogenic temperatures and only in isolated single dot system…
Non-reciprocal quantum interactions and devices via autonomous feed-forward
在最近的工作[A。Metelmann和A. A. Clerk，Phys.Rev.X5，021025（2015）]，描述了一种用于生成非互易量子相互作用和器件的通用量子工程方法。我们在这里展示了在许多情况下，这个一般的配方可以被看作是一个例子的自主前馈：完全耗散的演化是相同的设置中的无条件演化，其中一个观察者执行一个系统的理想量子测量，然后使用的结果来驱动第二个系统。我们还将这种方法的应用扩展到非互易量子放大器，显示使用两个工程水库时可能增加的功能。特别是，我们演示了如何构建一个理想的相位保持腔为基础的放大器，这是完全非互易，量子限制和任何基本的增益带宽的限制。
We have performed a quantum mechanical analysis of travelling-wave parametric amplifiers (TWPAs) in order to investigate five experimental phenomena related to their operations, namely the effect of impedance mismatch, the presence of upper idler modes, the presence of quantum and thermal noise, the generation of squeezed states, and the preservation of pre-squeezed states during amplification. Our analysis uses momentum operators to describe the spatial evolution of quantised modes along a TWPA. We calculate the restriction placed on pump amplitude as well as amplifier gain as a result of imp…
Continuous variable dense coding under realistic non-ideal scenarios
Harish-Chandra Research Institute（哈里希-钱德拉研究所）；Homi Bhabha National Institute（霍米·巴哈国家研究所）；Dipartimento di Fisica “Aldo Pontremoli,” Università degli Studi di Milano（米兰大学阿尔多·蓬特罗莫利物理系）
The quantum volume test is a full-system benchmark for quantum computers that is sensitive to qubit number, fidelity, connectivity, and other quantities believed to be important in building useful devices. The test was designed to produce a single-number measure of a quantum computer's general capability, but a complete understanding of its limitations and operational meaning is still missing. We explore the quantum volume test to better understand its design aspects, sensitivity to errors, passing criteria, and what passing implies about a quantum computer. We elucidate some transient behavio…
Investigating the performance of RPM JTWPAs by optimizing LC-resonator elements
National Institute of Advanced Industrial Science and Technology (AIST)（先进产业科学技术研究所）；Global Research and Development Center for Business by Quantum-AI technology (G-QuAT)（量子AI技术商业全球研发中心）
