A References: continuum approximation of discrete sums?

yucheng
Messages
232
Reaction score
57
Is there more references for how accurate is the continuum approximation to discrete sums? Perhaps more mathematical.

What I've found:
https://lonitch.github.io/Sum-to-Int/
https://arxiv.org/pdf/2102.10941.pdf

Some examples are:
Sum to integral
$$\sum_{\mathbf{k}} \to 2 \left ( \frac{L}{2 \pi} \right ) \int d^3k$$

Density of oscillator modes etc
 
Physics news on Phys.org
Here is Terry Tao discussing the Euler-Maclaurin formula mentioned in your arxiv link: link.

EDIT: Also, is there a reason you posted this in the Quantum subforum?
 
Haborix said:
EDIT: Also, is there a reason you posted this in the Quantum subforum?
Thanks!

Yes it appears in many places in Quantum optics, so I was hoping that there is a less mathematically abstract analysis, especially that of the error in the approximation (for instance, applying it to a model physical system, comparing the exact sum vs continuum approximation), whether it causes deviations from experimental results.....

P.S. the zeta functions, bernoulli functions makes me want to cry, but if that's what's needed, then I'll have to slowly crawl my way there...
 
I did find one! Serendipity!

Fermi's golden rule: its derivation and breakdown by an ideal model by J. M. Zhang, Y. Liu

Search in document:
in replacing the summation by an integral, the sampling step-length
https://arxiv.org/pdf/1604.06916.pdf
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA
I am reading WHAT IS A QUANTUM FIELD THEORY?" A First Introduction for Mathematicians. The author states (2.4 Finite versus Continuous Models) that the use of continuity causes the infinities in QFT: 'Mathematicians are trained to think of physical space as R3. But our continuous model of physical space as R3 is of course an idealization, both at the scale of the very large and at the scale of the very small. This idealization has proved to be very powerful, but in the case of Quantum...
Thread 'Lesser Green's function'
The lesser Green's function is defined as: $$G^{<}(t,t')=i\langle C_{\nu}^{\dagger}(t')C_{\nu}(t)\rangle=i\bra{n}C_{\nu}^{\dagger}(t')C_{\nu}(t)\ket{n}$$ where ##\ket{n}## is the many particle ground state. $$G^{<}(t,t')=i\bra{n}e^{iHt'}C_{\nu}^{\dagger}(0)e^{-iHt'}e^{iHt}C_{\nu}(0)e^{-iHt}\ket{n}$$ First consider the case t <t' Define, $$\ket{\alpha}=e^{-iH(t'-t)}C_{\nu}(0)e^{-iHt}\ket{n}$$ $$\ket{\beta}=C_{\nu}(0)e^{-iHt'}\ket{n}$$ $$G^{<}(t,t')=i\bra{\beta}\ket{\alpha}$$ ##\ket{\alpha}##...
Back
Top