Using existing experimental and computational equipment, a multi-institutional team has developed an efficient method for measuring high frequency qudits (Now Qubits become Qudits) attached to frequency combs, which are a type of photon source, in a single optical burst.
Although the word “qudit” may seem like a typo, the unknown cousin of the qubit, or quantum bit, can carry more information and is more sensitive to noise – two important qualities is necessary to improve the performance of quantum networks. , quantum distributed systems and, finally, the quantum internet.
Classical microcomputers classify data as one or zero, while qubits can hold the values of one, zero, or two – at the same time – due to the large state, which is what allows for many quantum states to exist at the same time. The “d” in qudit represents the number of different levels or patterns that can be encoded in a photon. Traditional qubits have two levels, but adding more levels turns them into qudits.
Recently, researchers from the Department of Energy’s Oak Ridge National Laboratory, Purdue University, and École Polytechnique Fédérale de Lausanne, or EPFL, successfully demonstrated a pair of interconnected eight-level qudits, which created a space of 64 square-square-meters – four times the size of the previous one, record for a unique frequency spectrum. The results were published in Nature Communications.
“We always knew that it would be possible to encode qudits of the order of 10 or 20 or more using the color of photons, or optics, but the problem is that measuring these things is difficult,” said Hsuan-Hao Lu, a postdoctoral researcher. at ORNL. “That’s the value of this article – we’ve discovered an effective, novel approach that’s easy to implement in the experimental setting.”
Qudits also tend to grow when paired, meaning they share a non-classic relationship regardless of the distance between them. Despite these challenges, qubits — two qubits in the form of photons that overlap in their frequency — are well-suited for transmitting quantum information because they can follow a prescribed path through an optical fiber without a great change from their environment.
“We combined modern frequency production with modern light sources, and used our method to define a high-quality qudit connection with a level of accuracy that has not been shown before,” said. Joseph Lukens, Wigner Fellow and researcher at ORNL.
The researchers began their experiment by injecting a laser into a micro-ring resonator – a circular device in a chip made by EPFL and made to achieve non-classical light. The source of powerful photons takes up 1 square millimeter – about the size of the tip of a sharp pencil – and allows the team to create binary numbers in the form of repeated combs.
Typically, qudit experiments require researchers to build a type of quantum circuit called a quantum gate. But in this case, the team used an electro-optical modulator that mixes different lights with a pulse generator to change the part of the frequencies. These techniques are being studied extensively at the Ultrafast Optics and Fiber Optic Communications Laboratory directed by Andrew Weiner at Purdue, where Lu studied before joining ORNL.
These visual aids are common in the media industry, and researchers have built these random projects to capture many different frequency connections. According to Lu, the process is like rolling a pair of six-sided dice and recording how often each combination of numbers comes up – but now the dice are aligned with each other.
This system, which includes time-shifters and signal shapers, is based on the classical method of ultrafast, broadband photonic signal processing and extended to the method of frequency qudits,” said Weiner.
To work backwards and extract which quantum states produced good frequency correlations for the qudit application, the researchers developed a data analysis tool based on a statistical method called Bayesian inference and ran computer simulations at ORNL. This achievement builds on previous work by this group focused on performing Bayesian analysis and quantum state simulation.
The researchers are now fine-tuning their measurement methods to prepare for the experimental procedure. By sending signals through fiber optics, they aim to test quantum communication methods such as teleportation, which is a method of transferring quantum information, and ring coupling, which is a method of connecting two particles that have not previously been separated.
Karthik Myilswamy, a graduate student at Purdue, plans to bring the micro-ring resonator to ORNL, which will allow the team to test these capabilities in a regional network of labs.
“Now that we have a method to know exactly the frequency of qudits, we can do more experiments depending on the application,” Myilswamy said.
