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A Schrodinger Cat Living in Two Boxes (1601.05505v1)

Published 21 Jan 2016 in quant-ph

Abstract: Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as "cat states", have been an elegant demonstration of Schrodinger's famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states. We present full quantum state tomography of this complex cat state over a Hilbert space exceeding 100 dimensions via quantum non-demolition measurements of the joint photon number parity. The ability to manipulate such multi-cavity quantum states paves the way for logical operations between redundantly encoded qubits for fault-tolerant quantum computation and communication.

Citations (304)

Summary

  • The paper presents the creation of a two-mode cat state via controlled dispersive interactions between superconducting microwave cavities and a transmon qubit.
  • It employs full quantum state tomography over a Hilbert space exceeding 100 dimensions, revealing strong Wigner negativity and high state fidelity.
  • The research suggests that the robust two-mode cat state can enable redundant qubit encoding for scalable, fault-tolerant quantum computing and advanced error correction.

Analysis of "A Schrödinger Cat Living in Two Boxes"

The paper entitled "A Schrödinger Cat Living in Two Boxes" presents an insightful contribution to the field of quantum information processing and communication, specifically through the implementation of quantum superpositions within a large Hilbert space. The authors demonstrate the creation and manipulation of a two-mode cat state in superconducting microwave cavities, utilizing a superconducting artificial atom (a transmon qubit) to bridge these cavities. By advancing this architecture, the research provides substantial implications for fault-tolerant quantum computation and the scaling of quantum systems.

Summary of Contributions

The authors successfully create a "two-mode cat state," essentially an entangled coherent state spanning two microwave cavities, representing an advance over traditional single-mode cat states. This involves the construction of multi-mode entangled states, allowing exploration of quantum superpositions at a larger scale. The primary result is achieved through the controlled dispersive interaction in a system with two cavity modes and a superconducting transmon.

Key contributions include:

  • Quantum State Tomography: Full quantum state tomography is performed over a high-dimensional Hilbert space, exceeding 100 dimensions. This is achieved using quantum non-demolition (QND) measurements of joint photon number parity.
  • State Characterization and Fidelity: The research demonstrates strong Wigner negativity and non-classical correlations, with a joint parity measurement showing values close to the theoretical expectations. The measured parity of -0.81 out of an ideal -1 for the odd-parity state underscores the achieved control over quantum states.
  • Implications for Quantum Computation: The entangled state achieved is suitable for encoding qubits redundantly and showcases potential for quantum error correction. The work may facilitate logical operations between these encoded qubits, a step toward fault-tolerant quantum computing.

Experiment Overview

The experimental setup utilizes a complex system where two high-quality (high-Q) 3D superconducting microwave cavities and a transmon qubit interact to form the entangled cat state. The distinctive feature is the deterministic creation of a two-mode cat state, enhanced by the advanced control of the transmon's three energy levels for photon-number parity operations.

Parameters of interest include:

  • Transition frequencies and coherence times for the involved components.
  • Dispersive shifts that allow for high-fidelity control.
  • The resulting cat states uphold configurability in coherence levels within the experiment’s constraints.

The use of these parameters enables the precise generation and evaluation of the cat states, with coherent state separation indicating a significant advancement in scalable quantum information processing.

Implications and Future Research Directions

The methodology showcased sets a new benchmark for creating macroscopic quantum states across multiple modes and could have extensive ramifications for quantum metrology, networks, and computational architecture. The quantum system's high-dimensional control offers a pathway to perform error correction beyond current capabilities, potentially leading to robust quantum information systems.

The future exploration can focus on:

  • Scaled-up Quantum States: Extending the dimensionality and complexity of these states to encompass more cavities, contributing to diverse quantum computing architectures.
  • Improved Error Correction Schemes: Enhancing the fidelity and error correction dynamics within this framework to approach or exceed existing benchmarks.
  • Integrated Quantum Networks: Leveraging these states in quantum networks for entanglement distribution and secure quantum communication.

In conclusion, this research stands as a significant demonstration in the construction and characterization of a two-mode cat state, paving the way for scalable quantum computing systems with enhanced fault tolerance and potential for complex quantum communications networks.