https://haifei.pro/en/tags/quantum-information/Recent content in Quantum Information on Haifei's HomeHugoenhfwang132@gmail.com (hfwang132)hfwang132@gmail.com (hfwang132)This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.Tue, 08 Oct 2024 11:36:44 +0800https://haifei.pro/en/post_20241008_%E9%87%8F%E5%AD%90%E6%80%81-%E7%AE%97%E7%AC%A6%E7%9A%84-weyl-%E5%92%8C-wigner-%E8%A1%A8%E7%A4%BA/Tue, 08 Oct 2024 11:36:44 +0800hfwang132@gmail.com (hfwang132)https://haifei.pro/en/post_20241008_%E9%87%8F%E5%AD%90%E6%80%81-%E7%AE%97%E7%AC%A6%E7%9A%84-weyl-%E5%92%8C-wigner-%E8%A1%A8%E7%A4%BA/<h2 id="preface">Preface</h2> <p>In classical mechanics, a physical quantity is a function on phase space, while the state of a system is a point in phase space (or, for an ensemble, a probability distribution on phase space). Upon quantizing this language, one obtains the phase-space representation of quantum states/operators, namely the Wigner representation. The Weyl representation is its Fourier transform.</p> <p>Most authors define the Wigner representation as:</p> \[F_W(x,p)=\int \mathrm{d}y \langle x+\frac{y}{2}\mid F \mid x - \frac{y}{2} \rangle e^{\mathrm{i} p y}\]<p>and then derive its various properties. However, from a physicist&rsquo;s perspective, the physical meaning of this expression is unclear, and \((x,p)\) do not have equal status, which is somewhat uncomfortable to look at.</p>https://haifei.pro/en/post_20240522_%E9%87%8F%E5%AD%90%E7%BA%A0%E7%BC%A0%E7%9A%84%E9%80%9F%E5%BA%A6%E6%98%AF%E5%90%A6%E8%B6%85%E8%BF%87%E5%85%89%E9%80%9F/Wed, 22 May 2024 14:50:35 +0800hfwang132@gmail.com (hfwang132)https://haifei.pro/en/post_20240522_%E9%87%8F%E5%AD%90%E7%BA%A0%E7%BC%A0%E7%9A%84%E9%80%9F%E5%BA%A6%E6%98%AF%E5%90%A6%E8%B6%85%E8%BF%87%E5%85%89%E9%80%9F/<p>Too long; didn&rsquo;t read version:</p> <p>&ldquo;Spooky action at a distance (superluminal)&rdquo; is an outdated view. According to special relativity, there is no interaction between events at spacelike separation. The mainstream view in academia is to consider quantum states and measurement bases together as reality, known as contextuality. Nonlocality is a corollary of contextuality.</p> <hr> <p>Body:</p> <p>Discussing the &ldquo;speed&rdquo; of quantum entanglement is meaningless.</p> <p>If the distance between two measurement events a and b is spacelike, then a is neither in the past nor in the future of b.</p>