Physlab’s Single Photon Quantum Mechanics and Quantum Information Lab

Our Book

Online ISBN: 978-0-7503-3063-3 Print ISBN: 978-0-7503-3061-9

Quantum Mechanics in the Single Photon Laboratory

Abstract

Arising from a series of laboratory class experiments developed by the authors this book provides an overview of fundamental experiments that can be used to practically demonstrate the underlying principles of quantum physics and quantum information science. Designed with multiple readerships in mind, it will be essential for the professor who would like to recreate a similar suite of experiments for their students and students of physics, who would like to learn how such experiments are actually conducted. Computer scientists, photonics engineers, and electrical engineers who would like to foray into quantum technologies would also find this narrative useful to learn about the terminology, key postulates of quantum physics, the collapse of states on measurement, and how quantum computers could be implemented.

Quantum computing holds great promise for the next wave of the information revolution. A number of physical platforms are available to realize quantum bits (qubits), including those based on nuclear magnetic resonance, trapped ions, superconductors, spin-1/2 particles, and single photons. Qubits based on photons are readily accessible at room temperature and hence can be used to perform experiments in the undergraduate laboratory.

The “Single Photon Quantum” initiative is our effort to develop a laboratory incorporating modern, cost-effective versions of some of the experiments that have shaped our modern understanding of quantum physics (or if you like to call it, quantum ‘mechanics’, or quantum ‘information’). These experiments include quantitative demonstrations of the existence of single photons, tests of Bell’s inequalities, single-photon interference, quantum eraser, and quantum state tomography.

Here is a technical summary. In the Single Photon Quantum Lab, we generate single-photon pairs through type I spontaneous parametric downconversion and develop an FPGA based coincidence counting unit to count single photons and coincidence events. We measure the second-order correlation function of heralded single photons and demonstrate the quantum nature of light. We then generate a number of polarization-encoded single-qubit states and estimate them by performing a set of measurements. We also investigate the principle of complementarity by observing quantum erasure in a single photon interferometer. Furthermore, we generate two-qubit entangled states and perform three tests of local realism. Finally, we perform two-qubit quantum state tomography and obtain density matrices for a few states.

What is special about Physlab’s Single-Photon Quantum Lab? A laboratory course based on these experiments can complement and awaken traditional quantum mechanics courses and help students prepare for research in quantum optics, quantum computing, quantum information, and foundations of quantum mechanics. The laboratory also rests on an advanced collection of ideas in optics, data processing, embedded systems. Hence it is a truly inter-disciplinary blend, forming a sandbox for investigating cutting-edge research questions in quantum information. To the best of our knowledge, ours is the first such lab in Pakistan and we are not aware of similar efforts in the region. As technology continues to advance, it is expected that more institutions will be able to set up their versions of quantum mechanics labs very soon.

Hallmarks We would like to mention here some important hallmarks of Physlab’s Single Photon Quantum Lab.

a) is modular: one experiment builds on the other	b) no need for expensive coincidence units; use an FPGA and we will provide the code	c) full documentation available with pictorial guidelines available
d) tool to learn quantum mechanics, quantum optics and quantum information	e) tool to learn practical optics, electronics, instrumentation and embedded programming	f) sandbox for research in single-photon based quantum computing
g) blueprints are available; one can easily replicate	h) housed in Physlab which has an open policy for students and teachers from across the spectrum (in fact Hamza and Faizan were visiting students in Sabieh’s Physlab; Bilal was a BS student, Sabita, Hafsa and Umair are MS students and Mahid Anjum is an intern and student of Physics at the University of Nottingham, UK)	i) product of a student-faculty partnership

The Experiments

You can read our recently published book “Quantum Mechanics in the Single Photon Laboratory” which describes in considerable detail our experiments, background theory, recipes for replicating these experiments, the results, discussion, conclusions, FPGA codes and a complete shopping list of equipment needed to reproduce these experiments. However, recently (2022) we have upgraded the FPGA and the computer codes, letting away with Labview and migrating to Python. My student Bilal’s work on FPGA re-envisioning can be seen here.

Supplementary Material

In September 2023, we made a quantum random number generator out of the counts information received from a downconverted source. Here is a brief description of this random generator. The generators passes all NIST tests.
Commented FPGA code (original 2019)
LabVIEW files
Sample results (2019)
Inventory
FPGA main file (original 2019)
Verilog, Python codes, retrieved data (data from 2022, Nexys 4 FPGA, Excelitas single photon counters)
“Exploring Quantum Peculiarities” report by Mahid Anjum (2023)
Hardy’s Test and CHSH Test of Local Realism (report from Najeebullah, MS student 2023)
Presentation at the Frontiers in Physics, 1-3 December 2022, GCU Lahore
Presentation at the International Nathiagali Spring College, 24-28 July 2024

The experiments are divided into three categories.

A) Nature of photon and quantumness of light

Q1: Spontaneous Parametric Downconversion
Q2: Proof of Existence of Photons
Q3: Polarization State Estimation of Single Photons
Q4: Polarization Pattern Measurement of Single Photons
Q5: Single Photon Interference and Quantum Erasure
Q+NL: Nonlocal Version of Quantum Erasure

B) Entanglement and non-locality

NL1: Freedman’s Test of Local Realism
NL2: Hardy’s Test of Local Realism
NL3: CHSH Test of Local Realism

C) Variants of quantum state measurement on one and two qubits

QST: Quantum State Tomography