Quantum Physics

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A blog dedicated to physics; especially quantum physics.

Quantum Physics

1M ago

It’s been silent on my blog for a while now - the past year has been a busy time for me since I was working on my Master’s thesis as well as working as a research assistant at Fraunhofer in parallel. Both were great experiences but it became so time-consuming that I totally lost track of posting any content on this blog!
In April 24 I finished my Master’s Thesis in Physics in which I was mainly working on tensor networks. We tried to make DMRG (Density Matrix Renormalization Group) for Quantum Chemistry-like setups more efficient by lifting degeneracies in the symmetry sectors of the tensor n ..read more

Quantum Physics

1y ago

Recently, I briefly introduced what circuit cutting is, why it is an advisable thing to do with current quantum hardware (NISQ devices) and what additional costs the cutting is causing. However, I did not go into detail how such a circuit cutting method can look like in detail - this is what this entry will be about. In particular, we will have a look on the circuit cutting procedure proposed by Lowe et. al. [1] in which randomly applied channels are able to cut a circuit.
Identity on Cut Circuits
As mentioned in the previous entry, circuit cutting requires to find a proper identity channel o ..read more

Quantum Physics

1y ago

Even though quantum computing is a promising and huge field, it is still at an early development stage. We know algorithms with clear advantage towards classical algorithms such as Grover’s or Shor’s - however, we are far away from implementing those algorithms on real devices for e.g. breaking state of the art RSA encriptions.
Today’s Possibilities of Quantum Computing
Thus, part of current research is to make use of the kind of quantum computers which are available today: Noisy Intermediate-Scale Quantum (NISQ) devices. They are far away from ideal quantum computers since they provide only ..read more

Quantum Physics

1y ago

Last time we introduced basic definitions and a small set of rules of the ZX calculus. While our aim is to analyze the Bell circuit in terms of this framework, you can find more sophisticated examples in [2, pp. 28]. For the Bell circuit we only need one further ingredient:
Cups and Caps
Cups and Caps are the ZX-type representations of the Bell State |Φ^+>. As you surely know, this state “lives” in a four dimensional Hilbert space, and can be represented as a vector with four entries - and in the ZX calculus this means:
In more complicated circuits it is neat to know that this Bell state ..read more

Quantum Physics

1y ago

mysteriousquantumphysics:
I couldn’t resist to post this on Valentine’s Day, haha ..read more

Quantum Physics

1y ago

Recently, stumbled across a tensor network-type framework which was completely new to me - the ZX Calculus. The ZX Calculus is not only a neat way of representing possibly complicated mathematical equations, it also gives explicit rules to alter and simplify those expressions. The ZX Calculus is particularly suited to describe matters in quantum information, which is why I’d like to provide a neat example of how to use this framework. As you might already know, quantum circuits can be fully analysed and understood with the help of tensor networks (actually, they are tensor networks) [1]. Howe ..read more

Quantum Physics

1y ago

As I have mentioned in a previous entry, the past winter term I studied at Tsinghua University in Beijing. Unfortunately, I could not enter the country due to the Covid restrictions that have been still present when the semester started - nevertheless, I thought it might be valuable to share some experiences.
Studying Remotely
What had been a frustrating experience is that the exchange semester - which I had started organizing in summer 2021 - could not take place in person. The exchange semester started in September 22 and the information that exchange students cannot enter China was se ..read more

Quantum Physics

1y ago

Since the machine learning course I did this semester at Tsinghua university was mainly focused on typical data science applications, I was curious in how far those methods can be applied in physics. Of course it is nothing new that neural networks can in principle also be used for physical applications - however, tensor network methods still seem to be dominant in the field of numerical many body physics. Thus, I decided to dive in a little into the literature about the usage of Restrictive Boltzmann Machines (RBM) in many body physics.
What are RBMs?
Usually, RBMs are used for instance for ..read more