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Physicists at MIT have designed a quantum “light squeezer” that reduces quantum noise in an incoming laser beam by 15 percent. It is the first system of its kind to work at room temperature, making it amenable to a compact, portable setup that may be added to high-precision experiments to improve laser measurements where quantum noise is a limiting factor.

The heart of the new squeezer is a marble-sized optical cavity, housed in a vacuum chamber and containing two mirrors, one of which is smaller than the diameter of a human hair. The larger mirror stands stationary while the other is movable, suspended by a spring-like cantilever.

The shape and makeup of this second “nanomechanical” mirror is the key to the system’s ability to work at room temperature. When a laser beam enters the cavity, it bounces between the two mirrors. The force imparted by the light makes the nanomechanical mirror swing back and forth in a way that allows the researchers to engineer the light exiting the cavity to have special quantum properties.

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Quantum computers (QC) are poised to drive important advances in several domains, including medicine, material science and internet security. While current QC systems are small, several industry and academic efforts are underway to build large systems with many hundred qubits.

Towards this, computer scientists at Princeton University and physicists from Duke University collaborated to develop methods to design the next generation of quantum computers. Their study focused on QC systems built using trapped ion (TI) technology, which is one of the current front-running QC hardware technologies. By bringing together computer architecture techniques and device simulations, the team showed that co-designing near-term hardware with applications can potentially improve the reliability of TI systems by up to four orders of magnitude.

Continue reading “Examining trapped ion technology for next generation quantum computers” »

Quantum information scientists have introduced a new method for machine-learning classifications in quantum computing. The non-linear quantum kernels in a quantum binary classifier provide new insights for improving the accuracy of quantum machine learning, deemed able to outperform the current AI technology.

The research team led by Professor June-Koo Kevin Rhee from the School of Electrical Engineering, proposed a quantum classifier based on quantum state fidelity by using a different initial state and replacing the Hadamard classification with a swap test. Unlike the conventional approach, this method is expected to significantly enhance the classification tasks when the training dataset is small, by exploiting the quantum advantage in finding non-linear features in a large feature space.

Quantum machine learning holds promise as one of the imperative applications for quantum computing. In machine learning, one fundamental problem for a wide range of applications is classification, a task needed for recognizing patterns in labeled training data in order to assign a label to new, previously unseen data; and the kernel method has been an invaluable classification tool for identifying non-linear relationships in complex data.

Physicists at MIT have designed a quantum “light squeezer” that reduces quantum noise in an incoming laser beam by 15 percent. It is the first system of its kind to work at room temperature, making it amenable to a compact, portable setup that may be added to high-precision experiments to improve laser measurements where quantum noise is a limiting factor.

The heart of the new squeezer is a marble-sized optical cavity, housed in a vacuum chamber and containing two mirrors, one of which is smaller than the diameter of a human hair. The larger mirror stands stationary while the other is movable, suspended by a spring-like cantilever.

The shape and makeup of this second “nanomechanical” mirror is the key to the system’s ability to work at room temperature. When a laser beam enters the cavity, it bounces between the two mirrors. The force imparted by the light makes the nanomechanical mirror swing back and forth in a way that allows the researchers to engineer the light exiting the cavity to have special quantum properties.

By tuning the direction of the external magnetic field with respect to the crystallographic axis of the silicon wafer, an improvement of spin lifetime (relaxation time) by over two orders of magnitude was reported in silicon quantum dots. This breakthrough was carried out by a team led by academician Guo Guangcan from CAS Key Laboratory of Quantum Information, USTC, in which Prof. Guo Guoping, Prof. Li Hai-Ou with their colleagues and Origin Quantum Computing Company Limited. This work was published in Physical Review Letters on June 23, 2020.

Spin qubits based on silicon quantum dots have been a core issue in the development of large scale quantum computation due to its long coherence time and the compatibility with modern semiconductor technology. Recently, the relaxation time and dephasing time of spin qubits developed in Si MOS (Metal-Oxide-Semiconductor) and Si/SiGe heterostructure have surpassed hundreds of milliseconds and hundreds of microseconds, respectively, resulting in a single-qubit control fidelity over 99.9% and a two-qubit gate fidelity over 98%. With the success in college, labs and companies from the industry are starting to be involved in this field, such as Intel, CEA-Leti, and IMEC. However, the existence of valley states (a state associated with the dip in a particular electronic band) in silicon quantum dots could reduce spin relaxation time and dephasing time seriously via spin-valley mixing and limit the control fidelity of qubits.

Researchers at CRANN and Trinity’s School of Physics have created an innovative new device that will emit single particles of light, or photons, from quantum dots that are the key to practical quantum computers, quantum communications, and other quantum devices.

The team has made a significant improvement on previous designs in photonic systems via their device, which allows for controllable, directional emission of single photons and which produces entangled states of pairs of quantum dots.

Wiring a New Path to Scalable Quantum Computing

Last year, Google produced a 53-qubit quantum computer that could perform a specific calculation significantly faster than the world’s fastest supercomputer. Like most of today’s largest quantum computers, this system boasts tens of qubits—the quantum counterparts to bits, which encode information in conventional computers.

To make larger and more useful systems, most of today’s prototypes will have to overcome the challenges of stability and scalability. The latter will require increasing the density of signaling and wiring, which is hard to do without degrading the system’s stability. I believe a new circuit-wiring scheme developed over the last three years by RIKEN’s Superconducting Quantum Electronics Research Team, in collaboration with other institutes, opens the door to scaling up to 100 or more qubits within the next decade. Here, I discuss how.

Zero electrical resistance at room temperature? A material with this property, i.e. a room temperature superconductor, could revolutionize power distribution. But so far, the origin of superconductivity at high temperature is only incompletely understood. Scientists from Universität Hamburg and the Cluster of Excellence “CUI: Advanced Imaging of Matter” have succeeded in observing strong evidence of superfluidity in a central model system, a two-dimensional gas cloud for the first time. The scientists report on their experiments in the journal Science, which allow to investigate key issues of high-temperature superconductivity in a very well-controlled model system.

There are things that aren’t supposed to happen. For example, water cannot flow from one glass to another through the glass wall. Surprisingly, quantum mechanics allows this, provided the barrier between the two liquids is thin enough. Due to the quantum mechanical tunneling effect, particles can penetrate the barrier, even if the barrier is higher than the level of the liquids. Even more remarkably, this current can even flow when the level on both sides is the same or the current must flow slightly uphill. For this, however, the fluids on both sides must be superfluids, i.e. they must be able to flow around obstacles without friction.

This striking phenomenon was predicted by Brian Josephson during his doctoral thesis, and it is of such fundamental importance that he was awarded the Nobel Prize for it. The current is driven only by the wave nature of the superfluids and can, among other things, ensure that the superfluid begins to oscillate back and forth between the two sides—a phenomenon known as Josephson oscillations.

But lasers also show promise to do quite the opposite — to cool materials. Lasers that can cool materials could revolutionize fields ranging from bio-imaging to quantum communication.

In 2015, University of Washington researchers announced that they can use a laser to cool water and other liquids below room temperature. Now that same team has used a similar approach to refrigerate something quite different: a solid semiconductor. As the team shows in a paper published June 23 in Nature Communications, they could use an infrared laser to cool the solid semiconductor by at least 20 degrees C, or 36 F, below room temperature.

The device is a cantilever — similar to a diving board. Like a diving board after a swimmer jumps off into the water, the cantilever can vibrate at a specific frequency. But this cantilever doesn’t need a diver to vibrate. It can oscillate in response to thermal energy, or heat energy, at room temperature. Devices like these could make ideal optomechanical sensors, where their vibrations can be detected by a laser. But that laser also heats the cantilever, which dampens its performance.