All macroscopic quantum states are fragile and hard to prepare
arXiv:1805.09868 · doi:10.22331/q-2019-01-25-118
Abstract
We study the effect of local decoherence on arbitrary quantum states. Adapting techniques developed in quantum metrology, we show that the action of generic local noise processes -- though arbitrarily small -- always yields a state whose Quantum Fisher Information (QFI) with respect to local observables is linear in system size N, independent of the initial state. This implies that all macroscopic quantum states, which are characterized by a QFI that is quadratic in N, are fragile under decoherence, and cannot be maintained if the system is not perfectly isolated. We also provide analytical bounds on the effective system size, and show that the effective system size scales as the inverse of the noise parameter p for small p for all the noise channels considered, making it increasingly difficult to generate macroscopic or even mesoscopic quantum states. In turn, we also show that the preparation of a macroscopic quantum state, with respect to a conserved quantity, requires a device whose QFI is already at least as large as the one of the desired state. Given that the preparation device itself is classical and not a perfectly isolated macroscopic quantum state, the preparation device needs to be quadratically bigger than the macroscopic target state.
References in corpus (26)
- Decoherence, einselection, and the quantum origins of the classical
- Quantum-enhanced measurements: beating the standard quantum limit
- Quantum metrology
- General framework for estimating the ultimate precision limit in noisy quantum-enhanced metrology
- Detection of 15 dB Squeezed States of Light and their Application for the Absolute Calibration of Photoelectric Quantum Efficiency
- The elusive Heisenberg limit in quantum enhanced metrology
- A Schrodinger Cat Living in Two Boxes
- Improved quantum metrology using quantum error-correction
- Matter-wave interference with particles selected from a molecular library with masses exceeding 10000 amu
- Macroscopic quantum states: measures, fragility and implementations
- Efficient tools for quantum metrology with uncorrelated noise
- Adaptive quantum metrology under general Markovian noise
- Qubit metrology and decoherence
- Measures of macroscopicity for quantum spin systems
- Quantum metrology with full and fast quantum control
- On the effective size of certain "Schrödinger cat'' like states
- Theory of an Entanglement Laser
- A measurement-based measure of the size of macroscopic quantum superpositions
- Stability of quantum states of finite macroscopic systems against classical noises, perturbations from environments, and local measurements
- Coarse Graining Makes It Hard to See Micro-Macro Entanglement
- Macroscopic superpositions require tremendous measurement devices
- The size of quantum superpositions as measured with "classical" detectors
- How difficult it is to prove the quantumness of macroscropic states?
- Quantum Fisher Information as a Predictor of Decoherence in the Preparation of Spin-Cat States for Quantum Metrology
- Certifiability criterion for large-scale quantum systems
- On the limitations of a measurement-assisted optomechanical route to quantum macroscopicity of superposition states