Ultrafast Switch from a Bose-Einstein Condensate Matter - Practicalintroduction

reviewed by: Indrawan Vpp

A subpicosecond optical switch demonstrated in a semiconductor material moves researchers a step closer to an all-optical computer.


When “pumped” with an ultraviolet laser pulse, the microwire (light gray strip) acts as a microcavity containing quasiparticles called exciton polaritons that form a Bose-Einstein condensate (BEC). A red “control” pulse a few picoseconds later causes the BEC’s emitted light (purple beam, upper left) to shut off in less than a picosecond (sharp drop after first output pulse) before recovering moments later (wider output pulse). The “off” signal corresponds to the gap between the two output pulses. 

Light-based information-processing chips could provide a huge improvement in processing power and speed over today’s electronics, but one of the challenges to their development is creating optically-controlled switches that are fast. A new trick for allowing one light signal to control another in a semiconducting material now pushes switching times from around a picosecond (10−12 seconds) to as much as 100 times faster in a device that can be readily integrated onto a chip [1]. The rapid switching is achieved by exploiting a Bose-Einstein condensate (BEC)—a quantum state famous for exotic behavior in superconductors and cold gases—in a new way. The work paves the way to extremely high-frequency optical information technologies.

Optoelectronic switching—using light to control a current—has previously been demonstrated within just 1 femtosecond (10−12 seconds) but only in a semiconductor device that is difficult to fabricate and to operate [2]. A different approach to making chip-based optical devices exploits electronic excitations called exciton polaritons, formed when a photon trapped in an optical cavity interacts with an electronic state called an exciton (a combination of an electron and a “hole,” or absence of an electron). The photon and exciton can bind into a quasiparticle, the exciton polariton.

Exciton polaritons can interact with light in ways that change abruptly as the intensity of the light is changed. In particular, an optical pulse can cause the light emitted by these quasiparticles to decline abruptly to zero intensity. Polariton-based optical switches have been reported previously with switching times of a picosecond or so [3, 4].

A team in China led by Hui Li of East China Normal University wanted to speed up switching by using a BEC of polaritons, where the quasiparticles “condense” into a single quantum state. Bose-Einstein condensation generally happens only at ultralow temperatures, but exciton polaritons in semiconductor microcavities can form a BEC even at room temperature [5]. Such polariton condensates have been used before in optical switches and other devices [3, 6], but Li and colleagues suspected that they could achieve much faster switching with a new technique. They wanted to exploit the way a “control” pulse of light can interact with the photon part of the quasiparticles to rapidly clear many of the polaritons out of the BEC state and abruptly switch the system off.

The team’s polariton BEC is formed in a microcavity—a zinc oxide wire, 3.6 micrometers in cross-section—from exciton polaritons created by an ultraviolet pump pulse that lasts only a few femtoseconds. The pump photons bounce around within the wire’s hexagonal cross-section and interact with excitons in the material to form polaritons. The polaritons condense into a BEC of around 20 million quasiparticles that decays within a few picoseconds. The pump pulse serves as the input signal; while the BEC lasts, some of its photons are emitted and can be detected as the output.

The control pulse from a red laser disrupts the condensate, depleting it of polaritons and switching off the output signal. Li says that this disruption happens in less than a picosecond—about 100 times faster than earlier polariton switches. What is more, the ratio of on-to-off signal (extinction ratio) in the device is about a million—the best achieved in a polariton switch. The researchers say that the switching speed might be sped up by 10 times by shortening the duration of the control pulse.

“This is very nice work, and I’m impressed by their results,” says quantum optics expert Daniel Suárez Forero of the University of Maryland in College Park. “It is nice to see how, 27 years after the first experimental demonstration of a BEC, the control of systems hosting this phenomenon has improved to the point that technological applications can be implemented.”

He praises the room temperature operation, fast switching times, and high extinction ratio of the device. Such properties “make these systems very suitable for ultrafast switching technologies,” he says. But Suárez Forero cautions that there are still important challenges to overcome—for example, miniaturizing all the components of the setup, including the lasers.

References :

A. Schiffrin et al., “Optical-field-induced current in dielectrics,” Nature 493, 70 (2012).

C. Antón et al., “Dynamics of a polariton condensate transistor switch,” Appl. Phys. Lett. 101, 261116 (2012).

J. Feng et al., “All-optical switching based on interacting exciton polaritons in self-assembled perovskite microwires,” Sci. Adv. 7 (2021).


New Update 2022 - Knight-Hennessy scholars Stanford University

 Meet the 2022 Cohort


The scholars in the 2022 cohort come from 27 countries, including the first scholars from Belgium, Jamaica, Japan, Libya, North Macedonia, Peru, Saudi Arabia, Serbia, South Africa, Tanzania, and Vietnam. They have earned degrees from 42 institutions, including 13 outside of the United States. At Stanford, they will pursue graduate degrees in 35 degree programs in all seven schools.

Why should you consider applying to join KHS?

A Multidisciplinary Cohort

Nearly 3,000 graduate students enroll at Stanford annually. Next year, more than 80 (growing to 100 over time) will be Knight-Hennessy scholars. Knight-Hennessy scholars span all seven schools at the university and bring a wide array of diverse academic experiences prior to enrolling at Stanford.  Knight-Hennessy scholars are surrounded by fellow Stanford graduate students solving complex problems from different disciplinary approaches.

A Multicultural Cohort 

Knight-Hennessy scholars have lived, studied, and worked in a wide array of communities and cities, colleges and universities, companies and organizations throughout the world. Knight-Hennessy scholars also bring varied cultural perspectives based on (but not limited to) sex and gender identity, race and ethnicity, sexual orientation, religion, socioeconomic status, veteran status, and more.  Each cohort includes a breadth of backgrounds, beliefs, lived experiences, and aspirations. This is a multicultural community united by independence of thought, purposeful leadership, and civic mindset.

Dates and Deadlines

When are the important dates and deadlines for your separate, concurrent Knight-Hennessy Scholars and Stanford applications?


Each incoming Knight-Hennessy scholar must also apply to, be accepted by, and enroll in a full-time Stanford graduate degree program.

If you have already been offered and deferred admission to enroll in a full-time Stanford graduate program in 2023, or you are a Stanford PhD student who started your PhD in 2022 and will begin your second year in 2023, then you must submit one application to Knight-Hennessy Scholars.

Otherwise, you must submit two separate but concurrent applications; one to Knight-Hennessy Scholars, and one to your Stanford graduate degree program. This applies both to candidates seeking admission to their first Stanford graduate degree program, as well as to current Stanford graduate students adding a second graduate degree.

Knight-Hennessy Scholars

You will submit an application to Knight-Hennessy Scholars. The Knight-Hennessy Scholars application opens in July and is due in October. The KHS application deadline in October is the same for all applicants, regardless of the Stanford degree program to which you will apply.

KHS Application Deadline: October 12, 2022, 1:00 pm Pacific Time

Last updated July 17, 2022

Stanford degree program

You will submit a completely separate application to your Stanford graduate degree program. Unlike the KHS application, which has a uniform deadline for everyone, the Stanford application deadlines vary by program. It is important to check with your desired program to confirm its deadline for KHS applicants, which may be earlier than its regular application deadline.

Stanford Degree Program Application Deadline: The Stanford degree program's application deadline or December 6, 2022, 1:00pm Pacific Time, whichever is earlier.  Visit the Stanford Graduate Admissions website to confirm the deadline for your program.


5 Travel Agencies in United States

5 Travel Agencies in United States

5 Travel Agencies in United States | What companies are the best travel agents in the United States? If you are going on vacation with your family or if you have work travel plans in different cities in the United States, however you do not know which travel agency you should choose, then you have nothing to worry about.  Because, in this article discussed about Travel Agencies in the United States, which you can make one of the choices that will accompany your trip, namely:

1. Citiair Travel Agent


Citiair Travel is a prestigious and highly well-known travel agency company in North America. This company presents tickets at very low prices, but with very satisfying facilities and services.

This travel agent has very complete customer service support 24 hours and 7 days a week. With this service, they are able to facilitate and connect communication between various travel agents and their customers.

This company is a very professional company and trained in the field of travel agents in the United States and also Canada.

2. Liberty Travel Agent


Liberty Travel is one of the travel agent services that has twice won awards from Newsweek in the best customer service category. 

Liberty travel agent will help you to get a new experience that will not be forgotten on your trip to the whole world. Of all liberty travel agent service products, the most favorite trip is a tourist visit to Shenandoah National Park located in Virginia, United States. In this case Liberty has a Skyland Resort vacation package with a vacation travel time of 3 nights, with ticket prices starting at $445.

3. Travel Leaders travel agent


Travel Leaders are experienced travel agents who provide customer service 24 hours a day. By using the services of this travel agent, you will be more able to adjust your budget to the travel package you will use.

In one travel package, you will get a variety of services, such as transportation accommodation, food and drinks, entertainment and tips, as well as taxes and other fees.

This travel agency company has been established and experienced for more than 75 years. It already has no less than 8,511 travel guides in the United States, and also 300 global associate companies. In addition, this company has also won 75 awards in the industrial field since 2009.

4. Take Tour travel agent


This travel company Based in the city of Boston, And already has no less than 7000 guided trips, complete packages and varied tourist destinations.

Take tour also offers no less than 2000 tourist destinations for you to explore around the world. Take Tours is the largest travel agency in the United States. This company serves tourists 24 hours a day, and 7 days a week.

Take Tour offers vacation packages and tourist trips throughout the United States, Canada, Mexico City, and even Europe. The cheapest Travel Packages within the famous country of the United States are: Grand Canyon tours, Niagara Falls tours, New York tours, Los Angeles tours, Yellowstone tours and San Francisco tours.

5. US-Tours and Travel-Corp


U.S. Tours and Travel Corp. is a travel agency that has also been established for many years. The company was founded in 1997, and still continues to operate today. 

The company offers a variety of national as well as international travel themes. For example, travel by cruise ship, train ticket services, student-only trips, religiously themed trips, family-only vacations, travel by car, visa and passport services, all of which are already included in every available tour package.


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