[Paper Review] Is a Single Photon Always Circularly Polarized? A Proposed Experiment using a Superconducting Microcalorimeter Photon Detector

Alan M. Kadin, Steven B. Kaplan|arXiv (Cornell University)|Jul 9, 2014

Quantum Information and Cryptography17 references4 citations

TL;DR

This paper proposes an experiment using a superconducting microcalorimeter with sub-eV energy resolution to test whether a single photon is inherently circularly polarized or can exist as a linearly polarized state. The method distinguishes single photons from photon pairs by measuring energy deposition with high precision, aiming to resolve a foundational quantum physics debate about photon spin and polarization, potentially challenging core concepts like quantum entanglement and nonlocality if linearly polarized photons are shown to be superpositions of circularly polarized states.

ABSTRACT

A single photon is well known to have spin S = hbar, which would correspond to circular polarization, and all quantum transitions with photon absorption or emission correspond to DeltaS = +/-hbar. However, it is also widely believed that a single photon may be linearly polarized, which would correspond to a state with S = 0. Indeed, linearly polarized single photons are central to most quantum entanglement experiments. On the contrary, it has recently been suggested (based on a realistic spin-quantized wave picture of quantum states) that a linearly polarized photon state must be a superposition of a pair of circularly polarized photons, each with S = +/-hbar. This question cannot be resolved using a conventional photon detector, which generally cannot distinguish one photon from two simultaneous photons. However, it can be addressed using a superconducting microcalorimeter detector with sub-eV energy resolution and high quantum efficiency (QE). A careful experiment demonstrating this photon pairing could place in question some of the paradoxical central foundations of modern quantum theory, including quantum entanglement and nonlocality.

Motivation & Objective

• To test the fundamental nature of photon polarization, specifically whether a single photon is always circularly polarized or can be linearly polarized.
• To resolve a long-standing debate in quantum physics about whether linearly polarized photons are superpositions of circularly polarized states with S = ±ħ.
• To investigate whether conventional photon detectors, which cannot distinguish single photons from photon pairs, invalidate interpretations of quantum entanglement and nonlocality.
• To demonstrate the feasibility of using high-resolution superconducting microcalorimeters to probe foundational quantum theory with single-photon energy measurements.
• To challenge the assumption that linearly polarized single photons are fundamental states, suggesting instead they are quantum superpositions of circularly polarized photons.

Proposed method

• Use a superconducting microcalorimeter with sub-eV energy resolution to detect individual photons with high quantum efficiency.
• Measure the energy deposition of incoming photons to distinguish between a single photon and two simultaneous photons, which would have double the energy.
• Irradiate the detector with a controlled source of linearly polarized single photons generated via parametric down-conversion or similar methods.
• Analyze the energy spectrum to detect whether the observed signal corresponds to one photon (energy E) or two photons (energy 2E), which would indicate the linearly polarized state is a superposition of two circularly polarized photons.
• Apply a realistic spin-quantized wave model of quantum states to interpret the results in terms of photon spin and polarization.
• Use the detector's high temporal and energy resolution to resolve the quantum nature of individual photon events with minimal ambiguity.

Experimental results

Research questions

• RQ1 Is a single photon fundamentally circularly polarized, with spin S = ħ, or can it exist as a linearly polarized state with S = 0?
• RQ2 Can a linearly polarized single photon state be experimentally shown to be a superposition of two circularly polarized photons, each with S = ±ħ?
• RQ3 Does the inability of conventional detectors to resolve single-photon events from photon pairs invalidate key assumptions in quantum entanglement and nonlocality?
• RQ4 Can a superconducting microcalorimeter with sub-eV energy resolution definitively distinguish between one photon and two photons in a single detection event?
• RQ5 What would be the implications for quantum foundations if linearly polarized photons are confirmed to be superpositions of circularly polarized states?

Key findings

• The proposed experiment can distinguish single photons from photon pairs with sub-eV energy resolution, enabling a direct test of photon polarization nature.
• If the detector registers energy E for a linearly polarized state, it supports the view that the state is a superposition of two circularly polarized photons with S = ±ħ.
• A detection of energy 2E would indicate two simultaneous photons, contradicting the assumption that a linearly polarized state is a single quantum entity.
• The experiment could challenge the foundational role of quantum entanglement and nonlocality if linearly polarized photons are shown to be composed of two circularly polarized photons.
• The outcome would depend on whether the energy deposition pattern matches a single photon or two photons, providing a decisive test of the spin-quantized wave model.
• The result may necessitate a reevaluation of quantum theory interpretations that assume linearly polarized single photons as fundamental states.