{"id":15905,"date":"2024-01-18T22:15:05","date_gmt":"2024-01-18T22:15:05","guid":{"rendered":"https:\/\/liquidinstruments.com\/?p=15905"},"modified":"2024-10-19T00:25:35","modified_gmt":"2024-10-19T00:25:35","slug":"introduction-to-quantum-optics","status":"publish","type":"post","link":"https:\/\/liquidinstruments.com\/blog\/introduction-to-quantum-optics\/","title":{"rendered":"An ultrafast introduction to quantum optics","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Quantum optics as a concept dates back to either 1900 or 1905, years when groundbreaking work in the realm of quantum mechanics was published by Max Planck<\/a> and Albert Einstein<\/a>, respectively. In Planck\u2019s case, he was working on a discrepancy that later became artfully known as the \u201c<\/span>ultraviolet catastrophe<\/span><\/a>.\u201d Planck\u2019s <\/span>solution<\/span> to this problem, in brief, was to assume that the energy of light was not a continuous spectrum \u2014 that it was instead organized into <\/span>quanta<\/span><\/i>. Einstein used this radical idea to explain another issue confounding physicists at the time, known as the <\/span>photoelectric effect<\/span><\/a>. His 1905 paper explaining this phenomenon was the first of his four <\/span>annus mirabilis <\/span><\/i>publications that year and earned him the <\/span>1921 Nobel Prize in Physics<\/span>.<\/span><\/p>\n

These quanta that Maxwell proposed and Einstein described are known as photons, and they are a key component of the wave-particle duality of light, an observation that revolutionized existing physics and essentially invented the entire field of quantum mechanics. The branch of quantum optics (QO) later grew out of this early work, seeking to further understand the quantum nature of light, particularly light as it interacts with matter. Over 100 years later, QO has grown into an enormous field of research with many of its own sub-fields, and earning many Nobel Prizes for its researchers.\u00a0<\/span><\/p>\n

Sub-fields of quantum optics: from sensing to computation<\/b><\/h2>\n

Quantum optics has many sub-fields; some of the most prominent are described below. This is not an exhaustive list, as new discoveries are being made every day. Additionally, research within a sub-field does not always fit into neat boxes \u2014 overlap of subject matter and\u00a0 experimental techniques are common.\u00a0<\/span><\/p>\n

Quantum information science (QIS)<\/h3>\n

QIS involves the study of quantum computing, communication, and cryptography. These fields typically utilize quantum states for information processing and secure data transmission. This has arguably been the most prominent application of quantum optics of the past decade, as the <\/span>2022 Nobel Prize in Physics<\/span> was awarded for work in the field of QIS. The last few years have also seen quantum computing transform from a niche academic topic into a large-scale industry. Even strictly staying within the bounds of optical quantum computing, many types of qubit systems are vying for supremacy, including <\/span>trapped ions<\/span>, <\/span>neutral atoms<\/span>, and <\/span>photonic processors<\/span>. Outside of computation, fields such as cryptography may see changes due to the promise of secure communications via <\/span>quantum key distribution<\/span><\/a> (QKD).<\/span><\/p>\n

Quantum metrology<\/h3>\n

This field <\/span>centers around the measurement of physical quantities using quantum properties such as superposition and entanglement, ultimately aiming for accuracy beyond classical limits. Applications include timekeeping with <\/span>optical atomic clocks<\/span><\/a>, <\/span>quantum sensing<\/span><\/a>, and <\/span>quantum holographic imaging<\/span><\/a>.<\/span><\/p>\n

Cavity quantum electrodynamics (CQED) <\/span><\/h3>\n

CQED studies the interaction between quantized light and matter within a cavity. Optical cavities make excellent spaces to isolate and preserve single atoms (either artificial or natural) and photons, allowing us to investigate phenomena like quantum entanglement and coherence. Groundbreaking work in CQED earned the <\/span>2012 Nobel Prize in Physics<\/span><\/a>. Although still an active field of research on its own, CQED techniques developed in the 1990s and 2000s played an integral part in the development of <\/span>modern quantum computer architecture<\/span>.\u00a0<\/span><\/p>\n

Quantum nonlinear optics (QNLO) <\/span><\/h3>\n

QNLO examines the interaction of light with matter in so-called <\/span>nonlinear media<\/span><\/i>, meaning a medium where the polarization responds non-linearly to an applied electric field. This usually can only be achieved at extremely high powers, a condition that modern lasers are able to meet. QNLO focuses on the effective interaction of individual <\/span>photons with other photons<\/span><\/a> in systems such as Rydberg atoms.\u00a0<\/span><\/p>\n

Ultrafast optics<\/h3>\n

This field deals with extremely short time-scale phenomena in quantum systems, typically on the order of 10<\/span>-15<\/span> (femtosecond) to 10<\/span>-18<\/span> (attosecond) scale. Pioneering work on the generation of ultrafast laser pulses recently won the <\/span>2023 Nobel Prize in Physics<\/span><\/a>. The pulses can be used to probe and control the dynamics of atoms and electrons, which occur on incredibly short timescales. Ultrafast laser pulses mean that they are also <\/span>intense in power<\/span>, which means that they are particularly useful for generating nonlinear behavior in materials (see the section on QNLO above).\u00a0<\/span><\/p>\n

The building blocks of quantum optics experiments\u00a0<\/b><\/h2>\n

While the range of experiments performed in this field is vast, there are some pieces of equipment that are common throughout many quantum optics labs.\u00a0<\/span><\/p>\n