Quantum Devices and Measurements

Osama M. Raisuddin, Suvranu De

Sergei Viznyuk

I expound on QM formalism, to reach conclusions on several topics of interest, and answer some questions:1. What is the amount of information in measuring device output?2. What determines the output of measuring device, aka quantum state?3. What is the amount of information required to set device to a certain configuration?4. What is the relation between preparation and measuring device?5. What is the relation between quantum state and quantum ensemble?6. Is there a boundary between measuring device and measured entity?7. Does quantum state (aka wave function) collapse upon measurement?8. Are event outcomes truly probabilistic as commonly believed?9. What is the significance of global phase?10. What is the boundary between measuring device and observer?11. What is the role of observer, debated since very inception of quantum mechanics?

K. Ismail, S Bandyopadhyay, Jean‐Pierre Leburton

M. J. Everitt, William J. Munro, Timothy P. Spiller

We study a non-linear quantum mechanical oscillator, acting as a measurement device. Candidate systems for realising such apparatus range from superconducting devices through to nano-mechanical resonators. The measurement device comprises an oscillator circuit where the dynamics of expectation values, in its correspondence limit, are either chaotic-like or periodic depending on the measured state of the quantum object – in this case a qubit. In a previous work we showed how the classical like trajectories of such a quantum system can act as a model of a projective measurement process. Here we investigate the quantum to classical transition of the measurement device and postulate criteria for realisation of an effective implementation of such a device.

Soumyajit Mandal

You-Qi Nie, Jian-Yu Guan, Hongyi Zhou +4 more

The randomness from a quantum random-number generator (QRNG) relies on the accurate characterization of its devices. However, device imperfections and inaccurate characterizations can result in wrong entropy estimation and bias in practice, which highly affects the genuine randomness generation and may even induce the disappearance of quantum randomness in an extreme case. Here we experimentally demonstrate a measurement-device-independent (MDI) QRNG based on time-bin encoding to achieve certified quantum randomness even when the measurement devices are uncharacterized and untrusted. The MDI-QRNG is randomly switched between the regular randomness generation mode and a test mode, in which four quantum states are randomly prepared to perform measurement tomography in real time. With a clock rate of 25 MHz, the MDI-QRNG generates a final random bit rate of 5.7 kbps. Such implementation with an all-fiber setup provides an approach to construct a fully integrated MDI-QRNG with trusted but error-prone devices in practice.